Nigel Farage has described the defection of Conservative candidate Mike Whitehead to Ukip as "another hammer blow to Tory pretensions in the north of England".
However, a Conservative Party spokesman dismissed Ukip's announcement as "cynical, misleading and utterly calculating to try and score political points".
David Cameron has urged potential Ukip voters to "come home" to the Conservatives on May 7.
The Prime Minister said the General Election was "not a time to send a message or make a protest" but to stop Ed Miliband and Labour forming a government.
Cameron said: "I would say to those people that I totally understand the frustration people have felt about issues like immigration where they want more done, and we will do more.
"And I understand the frustration about Europe - where the country deserves a referendum - and with me as Prime Minister they'll get that referendum.
"But this election is not a time to send a message or make a protest. This election is about choosing the government of our country for the next five years, and the choice could not be starker between a Conservative government led by me, continuing with a plan that's working, and putting it all at risk."
The Democratic presidential candidate may also have shown his cards on his choice of running mate.
The US president also shared a post on Twitter accusing Dr Anthony Fauci of misleading the public over hydroxychloroquine.
Fears over an impending second wave of coronavirus dominates Wednesday’s front pages.