The House of Lords has backed down in its opposition to the government's Bill allowing four all-postal voting pilots in this year's European and local elections.

The parliamentary ping-pong over the European Parliamentary and Local Elections (Pilots) Bill was the longest-running since 1998.

Both Conservatives and Liberal Democrats had opposed the move, arguing that it gave Labour an advantage over the other political parties, while the Electoral Commission had proposed that only two or three regions run the pilots.

It warned that the North West region was not yet ready for an all-postal poll.

The prime minister had said it was "absolutely extraordinary" that the House of Lords was overruling the will of the Commons.

"That would be wholly wrong and completely inconsistent with the proper conventions of the House," he argued.

But Liberal Democrat leader in the Lords, Baroness Williams, defended the actions of peers.

"The prime role of this House is not only to scrutinise legislation from another place but also to protect the fundamental liberties and rights of citizens in our constitution," she said.

"A very special responsibility rests on this House in relation to electoral matters, given that the majority in the Commons of almost all governments does not reflect a majority of views of electors."

However, on Thursday, peers voted by 138 votes to 108 to allow all four regions proposed by the government to hold all-postal votes in June, amid concerns that plans would not be set in place on time to hold the ballots.

Earlier this week constitutional affairs minister Chris Leslie had attacked peers' opposition to the legislation.

"I can barely believe that, despite the House of Commons reaching a strong view on so many occasions and so frequently expressing its opinion, we are still being told by the Conservative and Liberal majority in the House of Lords that it knows better than the House of Commons when it comes to elections policy," he said.