The Leave campaign broke the rules – there’s the justification for a Final Say, prime minister

As the parliamentary debate on the withdrawal agreement progresses, the call for a people’s vote becomes increasingly irresistible. A case in the High Court (Wilson and others v the prime minister) offers another argument in its favour: the government has a constitutional duty to at least re-consider whether it should proceed with Brexit.

All public bodies are subject to a legal duty, whenever they make a decision, to take all relevant considerations into account. This duty applies at every level, from district councils through to the prime minister. Where a public body fails to take a relevant consideration into account, its decision can be set aside.

The conduct of the Leave campaigns during the 2016 referendum is just such a relevant consideration. The Electoral Commission has found that Vote Leave incorrectly reported its spending and, in fact, exceed its spending limit by nearly 10 per cent. Spending limits are put in place to ensure that no side can “buy” an election. When Vote Leave exceeded its spending limit it gave itself, and by extension the entire Leave campaign, a significant unfair advantage. The Electoral Commission also found that Darren Grimes, founder of BeLeave misreported donations from Vote Leave and the campaign group “Veterans for Britain” also broke electoral rules. Grimes has denied any wrongdoing and is appealing the fine.

Organisations associated with the Leave side have also been fined by the information commissioner. The commissioner found that Leave.EU and Eldon Insurance, a company owned by Arron Banks, misused data belonging to Eldon’s customers and illegally sent 300,000 emails.

Whether the actions of those campaigning on behalf of Leave amount to criminal offences is a matter for the police, the director of Public Prosecutions and the courts. What can be said with certainty, however, is that two separate independent regulators have found that multiple organisations campaigning for a Leave vote, including the official Leave campaign, have committed serious breaches of either electoral law or privacy law.

Had such breaches been committed in a local election or a general election then they could have formed grounds on which to overturn the result of the election.

It is for the prime minister to take the final decision to ratify the withdrawal agreement (subject to the result of the meaningful vote and the passing of an Act of Parliament implementing the agreement). It was also for the prime minister to decide whether to conclude the withdrawal agreement. The fact that numerous organisations campaigning for a Leave vote broke the rules to such a significant extent is clearly a relevant fact that the prime minister should have taken into consideration when deciding to proceed with the withdrawal agreement. There is no evidence that the prime minister did so. Indeed, her public statements on the matter suggest that she did not.

Wilson and her fellow claimants argue that, in the light of the conduct of the Leave campaigns, first, the prime minister was wrong to act as though she was irrevocably bound by the result of the referendum, even if one side acted illegally. Second, that the prime minister wrongly proceeded on the basis that the actions of the Leave campaigns would not have made the result of the referendum void, when, in a local or general election it would have required the election to be re-run. Third, the prime minister was wrong to decide that the illegal actions of Leave campaigners didn’t invalidate the referendum result without first conducting a proper investigation.

Whether Ms Wilson succeeds or fails in her claim, the fact will remain that the result of the referendum is tainted by the Leave campaigners’ wrongful acts. The UK constitution is about more than the letter of the law. Unlike in America, where the Supreme Court has the final say about any constitutional question, the ultimate arbiter of the UK constitution is parliament. The responsibility, therefore, lies with parliament to protect the sanctity of our democracy by preventing the prime minister from forcing us to action the result of a referendum that is fundamentally flawed.

The 2016 referendum is often described as an “instruction” from the British people to the government. What should a responsible prime minister or parliament do when faced with an instruction that is so substantially tainted with illegality? The answer is clearly that she should seek a new instruction, in other words, a Final Say.

This is not the only argument in favour of a second referendum but it is undoubtedly a powerful one. Whichever side of the EU debate you fall on, it cannot be denied that leaving the EU is the most significant constitutional change in the UK’s recent history. To proceed on anything but an unimpeachable democratic mandate would be a catastrophic failure of governance, and an unforgivable betrayal of the electorate and the democratic principles at the foundation of our constitution.

Geraint Davies is the Labour member of Parliament for Swansea West. The article was written in collaboration with Daniel Leader who is a partner at Leigh Day LLP and Sam Fowles who is a barrister, member of Cornerstone Barristers, and a fellow at the Foreign Policy Centre