Nigel Farage has warned Britain is heading for a “half Brexit” after courts blocked the government triggering Article 50, promising to resume “full-time campaigning” if the process of leaving the European Union (EU) is not begun by spring.

On Thursday, the High Court ruled that the government must give parliament the final say on Brexit negotiations and the question of whether the UK pushes for a “soft Brexit” or “hard Brexit” – outside of the Single Market with full border controls.

Theresa May’s spokesman played down the ruling and insisted Article 50 would not be delayed, but leaders of the Vote Leave campaign said it was “reasonable” and told Brexit supporters to stop “whining”.

In an interview with BBC Radio 5 live, UKIP’s interim leader said: “We are heading for a half Brexit…. I’m becoming increasingly worried.

“I see MPs from all parties saying, oh well, actually we should stay part of the single market, we should continue with our daily financial contributions.

“I think we could be at the beginning, with this ruling, of a process where there is a deliberate, wilful attempt by our political class to betray 17.4 million voters.”

He also revealed: “I’m not going to disappear. If come spring of 2019 we haven’t left the EU, then I would have to take up full-time campaigning again.”

In a column for The Telegraph on Friday, he added: “There is now huge anger from those who went out on June 23 and voted to change our political system.

“They feel that their views are being totally ignored and their verdict thwarted by a rich elite who took the case to court, where unelected judges have struck a blow against Brexit.”

With a majority of just 15 in the House of Commons, only 8 Tory MPs need to rebel against the government’s position and side with Labour and the SNP to possibly block an Article 50 bill in parliament.

The government has promised to challenge Thursday’s ruling in the Supreme Court, but a number of Tory MPs are now urging Theresa May to call a snap general election to increase her majority and the chances of getting a bill passed.

Iain Duncan Smith, the former Work and Pensions Secretary, told The Times that Mrs. May would have “no other option but to go to the country” if MPs used legislation to prevent the start of formal talks or to wreck the negotiations.

However, Dominic Cummings, the campaign director of Vote Leave, urged Brexit supporters to accept the judgement because “at heart it is reasonable”.

He added that they should take a “deep breath and stick to important principles of how a serious country works” rather than “confused whining”.