Ukip leader Paul Nuttall is due to launch his by-election campaign in Stoke-on-Trent on Saturday.
The party is bidding to take its second seat in Westminster, in the poll called following the resignation of Labour MP Tristram Hunt.
Gareth Snell will attempt to hold Stoke-on-Trent Central for Labour as Ukip's leader hopes to capitalise on a strong Brexit vote in last year's EU referendum to secure himself a place in the Commons.
In the 2015 general election Labour had a 5,179 majority over Ukip, with the Tories third.
The by-election will be held on the same day as another contest in Copeland, triggered by the resignation of Labour MP Jamie Reed.