A shareholders agreement is a private, legally binding contract between a company's shareholders that sets out how the business is run, how shares can be transferred, and what happens if a founder leaves or a buyer comes calling. It sits alongside and fills the gaps in a company's articles of association and the Companies Act 2006, which on their own cover almost none of the situations that a shareholders agreement template actually break startups apart.
For UK founders, working out what a shareholders agreement is for, and whether you really need one, tends to happen at exactly the wrong moment: mid-argument with a co-founder, or mid-negotiation with a Series A investor who's just asked to see one. Get it in place before either happens, and it's a routine legal document. Leave it until afterwards, and it's a very expensive one.
What Is a Shareholders Agreement?
A shareholders agreement is a private contract between some or all of a company's shareholders and often the company itself that governs voting rights, share transfers, and what happens on exit, dispute or departure. Unlike the articles of association, which are filed publicly at Companies House, a shareholders agreement stays confidential between the parties who sign it.
It doesn't override the Companies Act 2006 or the company's constitution; it creates personal obligations between the shareholders who sign it, layered on top. Without one, a company falls back entirely on its articles of association (usually the Model Articles) and the Act itself, neither of which was written with a specific founding team, cap table or investor relationship in mind.
That gap matters more than it sounds. Under the Model Articles, both shareholder and board meetings typically only need a quorum of two, and there's no built-in mechanism to force a departing shareholder to sell their shares, break a voting deadlock, or stop a minority holder blocking a sale the majority wants. Founders who ask what a shareholders agreement actually adds, beyond what the law already gives them, usually get their answer the first time two shareholders disagree on something that matters.
Key Clauses: Drag-Along, Tag-Along, Pre-Emption
Three clauses do most of the heavy lifting in any UK shareholders agreement, and each solves a different failure mode. Drag-along rights let a majority shareholder usually a defined threshold of 51–75% force minority shareholders to sell on the same terms when the company is sold, so a single holdout can't block a deal the rest of the cap table wants.
None of this is automatic under UK company law; it only applies if it's written into the articles or the shareholders agreement. It's one of the clearest illustrations of what a shareholders agreement is actually for: without one, a departing co-founder keeps their full stake regardless of how or why they left, standard in UK practice, work the other way round: they let minority shareholders join a sale initiated by the majority, selling on the same price and terms rather than being left behind with a new controlling shareholder they never chose. Investors treat tag-along rights as a basic fairness mechanism in any UK shareholders agreement, and founders raising a round should expect to see both drag-along and tag-along sitting side by side — one protects the buyer's ability to get to 100%, the other protects the minority from being stranded.
Pre-emption rights are where founders most often confuse statute with contract. The Companies Act 2006 (s.561) already gives existing shareholders a statutory right of first refusal on newly issued ordinary shares, offered pro rata before anyone outside the company gets a look-in. What it doesn't cover is a share transfer if an existing shareholder wants to sell their stake to a third party, there's no automatic right for the others to buy first. That has to be written into the articles or the shareholders agreement directly, which is exactly why a generic shareholders agreement template pulled off the internet can leave a real gap: it may handle the statutory position on new shares perfectly well while saying nothing useful about what happens when someone wants to exit.
Good Leaver vs Bad Leaver Explained
Good leaver and bad leaver clauses decide what a departing shareholder walks away with, and the difference between the two categories can be the whole value of their stake. A good leaver, someone who leaves through redundancy, ill health, death or retirement typically keeps their vested shares, or is bought out at fair market value. A bad leaver, dismissed for cause such as fraud, gross misconduct or breach of a non-compete, usually forfeits unvested shares entirely and sells any vested shares back at nominal value, sometimes converted into worthless deferred shares.
None of this is automatic under UK company law; it only applies if it's written into the articles or the shareholders agreement. This is where the question of what is a shareholders agreement actually for gets a concrete answer: without one, a departing co-founder keeps their full stake regardless of how or why they left. The standard mechanism is reverse vesting over four years with a one-year cliff: founders legally hold their shares from day one, but the shares stay subject to forfeiture until they vest, which is precisely what stops a co-founder pocketing a third of the company after quitting in month four.
The one area that's genuinely shifted recently is voluntary resignation. UK Private Capital's (formerly the BVCA) model Series A documents the industry-standard templates most VC-backed rounds are built on removed voluntary resignation as an automatic bad leaver trigger in their February 2025 update, a meaningful softening from where the market sat even a couple of years earlier. Some early-stage investors still push to keep it in, but it's no longer the assumed default it once was.
What Investors Expect Before Series A
Before a Series A closes, UK investors expect a shareholders agreement built on the UK Private Capital (formerly BVCA) model documents the standardised suite of Subscription Agreement, Shareholders' Agreement and Articles of Association that the industry treats as the market baseline, and which the organisation itself says are designed specifically for Series A rounds rather than seed or later stages. Founders walking into a Series A conversation with a bare-bones shareholders agreement template, rather than something aligned to this standard, will usually be asked to redo it before term sheet negotiations get serious.
What investors typically want to see: founder warranties and disclosure obligations, drag-along provisions robust enough to survive a future exit, leaver provisions covering the founding team, anti-dilution protection against a future down round, and a defined list of reserved matters requiring investor consent before the board can act.
The February 2025 update to the model documents also added governance undertakings around anti-bribery, anti-money laundering and sanctions compliance a signal of how much more scrutiny due diligence now carries, even at early stage. None of this is a tick-box exercise for investors, and it's a good illustration of what is a shareholders agreement is worth to the people writing the cheque: it's the mechanism by which they protect a stake they can't easily sell in a company they don't control day to day.
Do You Need One as a Two-Founder Startup?
Two founders splitting a company 50/50 are, by most UK corporate lawyers' accounts, sitting on the single most common structural cause of startup deadlock. Neither shareholder can pass an ordinary resolution alone, neither can be outvoted, and the Companies Act 2006 provides no statutory mechanism to break the tie courts are reluctant to step in on internal disagreements, and the realistic options left are negotiation, a forced buy-out, or a costly unfair prejudice petition under section 994.
A shareholders agreement is where this gets solved before it becomes a problem: a casting vote for an independent director, a mandatory mediation step, or a Russian Roulette clause where one founder names a buy-out price and the other must either sell at it or buy at it. None of these clauses tends to sit in a basic shareholders agreement template by default, which is exactly why two-founder companies so often need to add them by hand rather than assume they're already covered.
Some founders sidestep the risk altogether by avoiding an exact 50/50 split in the first place. For a two-founder startup, what is a shareholders agreement really buying you? In effect, insurance against the possibility that you and your co-founder won't always agree however well things are going right now.
Conclusion
So, what is a shareholders agreement, boiled down to one line? It's the private rulebook that decides who controls what, who gets paid what, and who walks away with what, in every scenario the articles of association and the Companies Act 2006 don't cover.
For a UK startup, that's rarely optional in practice whether you're two founders splitting equity down the middle or a company heading into Series A with investors who'll expect one as standard. The businesses that get this right treat the shareholders agreement as founding infrastructure, not paperwork to sort out later.
FAQs
1. Do UK startups need a shareholders agreement?There's no legal requirement for a UK company to have one, but it's strongly recommended from day one of trading or whenever a new shareholder joins. Without it, the company relies entirely on the Model Articles and the Companies Act 2006, neither of which covers founder-specific issues like vesting, leaver terms or deadlock.
2. What should a shareholders agreement include?Core provisions typically cover governance and voting, share transfer rules (pre-emption, drag-along, tag-along), leaver clauses, dividend policy, and dispute resolution mechanisms such as deadlock and mediation procedures. A generic shareholders agreement template can provide a starting structure, but most UK solicitors recommend tailoring it to the specific cap table and investor relationships involved.
3. What happens if a startup doesn't have a shareholders agreement?The company defaults to its articles of association and the Companies Act 2006, which offer no deadlock-breaking mechanism, no compulsion for a departing shareholder to sell their shares, and no drag-along or tag-along rights the standard UK mechanisms for forcing through a clean exit. Disputes usually end up resolved through costly, uncertain routes like an unfair prejudice petition.
Also read: Why NHS Procurement Is Holding Back the UK's Best MedTech Startups
Sources: Companies Act 2006 (legislation.gov.uk); UK Private Capital (formerly BVCA) model document commentary via Davis Polk, Norton Rose Fulbright and HSF Kramer; leaver provision analysis via Bird & Bird and Ashfords; UK corporate solicitor guidance via Rocket Lawyer UK, Sprintlaw UK, Gilson Gray and SMEToday. Figures reflect the most recent available data at the time of writing.
The EP+ Editorial Desk covers UK startups, founder stories, and venture capital. All editorial content is independently produced and human-reviewed before publication.
