A committee of peers has slammed the policy-making process that led to the Legislative and Regulatory Reform Bill.
Thursday's report from the Lords constitution committee said ministers had failed to allow for proper pre-legislative scrutiny of the Bill.
The consultation process was also branded "lamentable" for failing to make clear the full extent of the government's proposals as they eventually emerged in the legislation.
This was described as "an indictment of the processes of policy-making and legislation".
Committee chairman Lord Holme said the government "got it badly wrong this time".
"They wanted to give themselves power to change any law with the minimum of parliamentary involvement, thus gold-plating their powers," Lord Holme said.
"They should have known that was constitutionally questionable."
He said the committee's main conclusion was that constitutional change should be made only by parliament through primary legislation, not ministers using delegated powers.
"The simple fact that ministers failed to recognise the profound constitutional importance of the Legislative and Regulatory Reform Bill does not inspire confidence that they would not use delegated powers to introduce constitutional change in the future, without even realising what they are doing," said Lord Holme.
"The way this Bill has been handled shows that with our unwritten constitution simple legislative proposals can drastically affect our law making system and the fundamental relationship between parliament and ministers.
"While we are pleased that the Bill has been improved to some degree in its passage through the Commons we are still not convinced that it strikes the right balance between enabling worthwhile legislation and ensuring effective parliamentary scrutiny."
