LONDON (REUTERS) - Britain will introduce a statutory register of political lobbyists, Deputy Prime Minister Nick Clegg said after three members of the upper house of parliament were suspended from their parties at the weekend in a "cash for access" scandal.

The three House of Lords peers were covertly filmed in a media sting offering to ask parliamentary questions, lobby ministers and host events in prestigious parliament premises in exchange for payment by what they were told were lobbyists acting for companies.

All three, two from the main opposition Labour Party and one from the Ulster Unionist Party, denied breaking the chamber's rules but their parties took swift action against them.

Another undercover media investigation had already forced a member of the lower house of parliament, Mr Patrick Mercer, to resign from the ruling Conservative Party and seek legal advice.

The government of Prime Minister David Cameron's Conservatives and its junior coalition partner the Liberal Democrats had pledged in 2010 to introduce the register, which would regulate lobbyists and give constituents the power to force lawmakers to resign in cases of serious misconduct.

But it was not mentioned by Queen Elizabeth in an annual speech in May setting out the government's legislative plans.

Mr Clegg, leader of the Liberal Democrats, said the government would press ahead with the reform.

"It will happen. Having consulted on the proposal, the detail is being looked at thoroughly in government," he wrote in the Daily Telegraph newspaper on Monday.