A parliamentary committee has rejected calls to clarify the informal conventions that govern the powers of the House of Lords.

It said there should be no move to set a limit on how long legislation can be delayed by the House of Lords.

Ministers had aimed to reach agreement that most bills should spend no longer than 60 sitting days in the upper house.

But the cross-party joint committee on conventions, chaired by Labour ex-cabinet minister Lord Cunningham, said there was no consensus on how long the time limit should be set at.

"There is no conventional definition of 'reasonable', and we do not recommend that one be invented," it said.

The Lords procedure committee could seek an "indicative" measure, but 80 sitting days would be more appropriate than 60.

And any such measure should be "flexible and unenforceable".

The committee concluded: "We do not recommend legislation, or any other form of codification which would turn conventions into rules, remove flexibility, exclude exceptions and inhibit evolution in response to political circumstances."

Lord Cunningham said that conventions "are flexible and unenforceable, and they do evolve as circumstances in parliament change".

"The House of Lords has the right to say 'no', and this report confirms that," he added.

Among its other findings, the report was also sceptical on how the Salisbury convention, under which peers do not reject legislation contained in the governing party's manifesto, could be adopted as a more formal procedural rule.

"We do not recommend any attempt to define a manifesto bill," the committee said. "Without such a definition, it will be clear that the resolution is flexible and unenforceable."

The report found "no scope" for codification of the rules for parliamentary 'ping pong'.

"All recommendations for the formulation or codification of conventions are subject to the current understanding that conventions as such are flexible and unenforceable, particularly in the self-regulating environment of the House of Lords," it added.

"Nothing in these recommendations would alter the present right of the House of Lords, in exceptional circumstances, to vote against the second reading or passing of any bill, or to vote down any statutory instrument where the parent act so provides.

"The courts have no role in adjudicating on possible breaches of parliamentary convention."