The Labour Party said that it would not be investigating the selection process in Brighton Kemptown.
It said that it had not received any complaints although Henry Smith, the Conservative MP for Crawley, has asked Sussex Police to investigate.
He asked the force to look into whether the Unite trade union had exerted undue influence over the selection procedures of local parties.
In Brighton Kemptown, one of 41 candidates being promoted by Unite, Nancy Platts, was chosen by local party members.
In another constituency, Falkirk, the party chairman and the candidate favoured by Unite have been suspended by the party.
It has been alleged that the union tried to rig the selection by joining union members to the Labour Party without their knowledge.
Mr Smith said that locally he wanted “assurances that the Unite union have not been allowed to sign up members without their knowledge as has been alleged in Falkirk”.
The union wanted two candidates chosen in Sussex – Nancy Platts in Brighton Kemptown and Simon Burgess in Hove.
Ms Platts was picked for the Brighton seat last month but another candidate, Peter Kyle, beat Mr Burgess in Hove.
A party insider said that the result in Hove showed that the party was not in the grip of Unite.
A spokesman said: “The Labour Party is not investigating any of the parliamentary selections in the South East of England and has not received any complaints about Brighton Kemptown.
“The Labour Party is committed to ensuring that selections are fair, open and run within the rules.
“Many of our candidates, like millions of hardworking people, are proud union members and recognise the work unions do to ensure fair treatment of employees.”
