A proposed bill to allow terminally ill adults in England and Wales to choose to end their lives failed on Friday as parliamentary time ran out, nearly a year since elected members of parliaments gave their backing.

Though the Terminally Ill Adults (End of Life) Bill was passed by the House of Commons last June, the UK’s revising chamber, the House of Lords, effectively talked it out since then.

Proponents of what has been termed “assisted dying” – sometimes referred to as “assisted suicide” – hoped it would mark the biggest change to social policy in the UK since abortion was partially legalised in 1967.

But opponents in the House of Lords have managed to hold up its passing by filing more than 1,200 amendments. That is believed to be a record high number for a piece of legislation that was tabled by a backbencher rather than by the government. Bills proposed by backbenchers can only be debated on a Friday, limiting the time available.

Campaigners for assisted dying have expressed their anger at the sight of unelected politicians holding up the will of the elected chamber. They have insisted that they intend to bring the bill back in the next parliamentary session, which begins after King Charles outlines the government’s coming programme in a speech to both houses of parliament on May 13.

The sponsor of the bill in the House of Lords, Charlie Falconer, said he felt “despondent” that a piece of legislation, which he said was “so important to so many, has not failed on its merits, but failed as a result of procedural wrangling”.