Brexit Party leader Nigel Farage has said changes must be made to the government's political declaration for his party to back Boris Johnson's deal.Mr Farage said his party will stand at least 600 candidates in the General Election unless the prime minister removes the allowance for the Brexit transition period to last until 2022."Boris Johnson is offering something that is not Brexit and does not get Brexit done," he told BBC Radio 4's Today programme.Mr Farage had previously said the prime minister had to scrap the Withdrawal Agreement for the Brexit Party to stand down candidates.Last week at the Brexit Party's election campaign launch, Mr Farage said his party would contest every seat unless Mr Johnson agreed to a "Leave alliance".But he told the BBC he wanted to see changes to the political declaration agreed with the EU."Boris Johnson needs to make it clear that he will fundamentally change the political declaration in two ways," he said."Firstly that he will get rid of an extension that will allow it to go on until at least 2022. We need to have the clause in the political declaration removed so we have a hard deadline."The second point is that we simply cannot, absolutely cannot, bind ourselves to a trade deal that gives us regulatory alignment that would prevent us from doing trade deals with the rest of the world and would mean we are not making our own laws."Mr Farage added that his party also needed to see any promises on regulatory alignment removed so Britain was not "prevented from doing trade deals and making our own laws".Pushed on Brexit Party candidates pulling out to back Conservatives, Mr Farage said it is usual for candidates to withdraw at the last minute due to the "huge amount of pressure".Mr Farage added: "I've never fought an election at which at the last minute candidates didn't pull out because they realise firstly the full responsibility of doing it and secondly they are coming under a huge amount of pressure."