Conservatives will support emergency legislation designed to clarify the Home Secretaryís ability to set minimum sentences for convicted murderers, Oliver Letwin has promised.

He made the pledge after a panel of seven Law Lords ruled that the Home Secretaryís power to increase the ìtariffî - or length of time - murderers must serve before applying for parole, was no longer compatible with human rights legislation.

The decision, in a test case brought by three convicted killers, could pave the way for appeals by 70 more prisoners who have already served the minimum sentences set at their trials, but who remain behind bars because of the additional time ordered by the Home Secretary.

Mr Letwin, the Shadow Home Secretary, was critical of the Law Lords ruling. ìIt is not a pleasing prospect that murderers who have committed appalling atrocities may be released before the date set by a Home Secretary who is accountable to public opinion,î he said.

And the Conservative shadow minister declared: ìWe will back moves by the Home Secretary to produce a short term solution for future sentences of such murderers.î But he also blamed the confusion on Labourís decision to force through controversial human rights legislation which has undermined Britainís domestic law.

ìThere is a deeper issue here. When it rushed through the Human Rights legislation, this government did not think of the implications - of which this is one. What is the effect of the ruling of incompatibility by the House of Lords? Can Parliament now uphold the tariffs set by Home Secretaries for existing prisoners or not?

ìWhat we have here is a frightful muddle brought about by the governmentís over-hasty approach to the fundamentals of British law. As I have been saying for months, there will be many other such implications. The time has come for Parliament as a whole to think through these implications properly and to ask what needs to be done to reassert Parliamentary sovereignty,î Mr Letwin added.