Keir Starmer has shown that Labour are holding the Tories to account over Brexit

MPs voted by a large majority tonight for a Labour motion requiring the Government to set out its plan for Brexit

Keir Starmer, shadow Brexit Secretary, in this afternoon's debate

The Labour Party has shown that it can still be an effective opposition. It has forced the Prime Minister to change her mind and agree to publish her plan for Brexit before the Government gives notice under Article 50 that the UK is leaving the EU.

Of course, that plan may not amount to much. Kenneth Clarke, the pro-EU former Chancellor, said witheringly in today’s debate: “We’ll be told that the ‘plan’ is to have a red, white and blue Brexit.”

But Labour has only three choices. It can accept Theresa May’s timetable, which is to trigger Article 50 by the end of March; or it can try to block or delay Article 50; or it can publicly adopt the first position while secretly trying to engineer the second.

Keir Starmer, the shadow Brexit Secretary, has chosen the first position, which is probably the right judgement. It would be difficult for the Opposition to argue against triggering Article 50, not least because Labour supported the referendum after the 2015 election. Labour MPs voted for the referendum Act knowing that it was the final choice, explicitly ruling out the possibility of a second referendum on the terms of the deal if the nation voted to leave.

David Davis, the Brexit Secretary, tried to suggest that Starmer was really going for position three – that he was pretending to agree to Article 50 but secretly trying to delay it. To which Starmer had the waspish reply that the timetable for publishing its plan and invoking Article 50 was the Government’s problem, not his.

Starmer has been an MP for only 19 months, but already he is leading for the Opposition on the most important subject to come before this parliament, and he is doing it with a skill and assurance that recalls the way John Smith, the Labour leader with 22 years’ parliamentary experience including as a cabinet minister, harried John Major’s government over the Maastricht Treaty in 1992-93.

Starmer presented himself as the advocate of the 48 per cent as well as the 52 per cent. “The vote on 23 June was not a vote to write those who voted to remain out of their own history,” he said.

He was quick on his feet, picking up a comment from Crispin Blunt, the Conservative MP, who said, “No plan survives contact with the enemy.” Starmer said it was wrong to describe our EU partners as “the enemy”.

But the secret of good opposition is not just speaking well in the Commons, although that is an important part of it. The more important part is preparation, and Starmer forced Theresa May’s U-turn by drafting his motion with care. By accepting Article 50 but asking for a plan first, he tempted enough Tory MPs to support his wording, forcing the Government to accept his motion and add its own amendment, which “calls on the Government to invoke Article 50 by 31 March 2017”.

That was designed to tie Labour firmly to the Government’s policy, to the evident disgust of Kenneth Clarke in this afternoon’s debate, who dismissed Labour’s motion as “harmless”. But it also undermines the Government’s case at the Supreme Court, because MPs will now vote explicitly on triggering Article 50. (Although David Pannick, counsel for Gina Miller, said today that his case is that Parliament has to pass an Act triggering Article 50, not just hold a vote.)

Which just goes to show that Theresa May made a political mistake in failing to ask Parliament to vote on Article 50 in the first place. Today, Keir Starmer made her pay for that mistake. The Labour motion, as amended by the Government, was voted through by a large majority, by 448 against 75 Scottish National Party MPs, the Liberal Democrats, a handful of Labour hard-Remainers and Kenneth Clarke.

Starmer’s parliamentary triumph in forcing a U-turn won’t satisfy those, such as Clarke, who want to block Brexit altogether, but it was a triumph all the same. He was able to claim: “Labour’s aim is to shape the debate and to head off hard Brexit.”