Nigel Farage and Chris Grayling will put on a united anti-EU front just days after Vote Leave won the lead 'leave' campaign designation from the Electoral Commission. The watchdog's ruling sparked discontent among rival Brexit group Leave.EU, with co-founder and Ukip donor Arron Banks threatening to launch a legal challenge.

But the businessman, who also backed Grassroots Out (GO), dropped his plan to take the Electoral Commission to court after consulting with Farage. The Ukip leader has promised to "work with anyone that wants to leave the EU" and will speak alongside Grayling, a Vote Leave campaigner and House of Commons leader, on 18 April in Stoke-on-Trent.

The top Conservative is expected to warn that a 'remain' vote at the 23 June ballot would be a green light for further EU integration, despite Prime Minister David Cameron's opt-out of 'ever closer union'.

"Things may seem a bit quiet in Brussels at the moment. There don't seem to be many new laws being brought forward," Grayling will say.

"But don't be deceived. It's not a sign that they have suddenly seen the light. They're holding it all back until we've voted, in the hope that we won't realise that there is another tidal wave of More Europe heading our way.

"A vote to remain isn't a vote for things the way they are today. It's a vote to be part of a relentless march of Europeanisation, with us less and less able to decide what's good for Britain. The European Commission's locker is full of new ideas and new plans. If we vote to remain, the door of that locker will be opened wide the day after."

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He will add: "I know that many here have different visions. Some are socialists and want a socialist government. I respect their right to campaign for their beliefs and to seek to elect a Labour administration.

"Above all, I respect the right of the British people to choose their government without interference from abroad. Across the world, the right of the peoples of nation states to elect – and throw out – governments is well established.

"The United States, Australia, Canada, Japan, India and South Africa all control their own destinies. Why should Britain, the mother of parliamentary democracy, be any different? Why should so many of our laws be made in Brussels, often against the wishes of the people we represent? It must change."

The speech will come just days before US President Barack Obama travels to the UK on 21 April to celebrate The Queen's 90th Birthday. The White House has revealed he will make a 'friendly' pro-EU intervention if he is quizzed by the media on the referendum during his visit, which will end on 24 April.

Latest EU referendum opinion polls

12-14 AprYouGov40%39%16%Online
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8-10 AprICM42%45%12%Online
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29 Mar-4 AprYouGov39%38%18%Online
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29 Mar–3 AprOBR51%44%5%Telephone
29 Mar - 1 AprOpinium39%42%18%Online