Three members of Britain's House of Lords are denying wrongdoing after apparently being caught in a newspaper sting agreeing to lobby Parliament in return for cash.

Labour peers Brian Mackenzie and Jack Cunningham and Ulster Unionist John Laird were recorded by Sunday Times reporters pretending to represent a solar energy firm. The men appeared to agree to push the firm's cause in Parliament.

On Friday, lawmaker Patrick Mercer left the Conservative party in Parliament ahead of allegations of lobbying irregularities due to be aired in a BBC documentary.

Mercer is alleged to have taken money from a fake firm professing to work for the government of Fiji.

British parliamentarians are barred from using their political positions to make a profit. Critics say the rules are too loose.