A committee of MPs has said it is "far from convinced" that government pans to tackle spiralling legal aid budgets will prove effective.

In a report published on Tuesday, the Commons constitutional affairs select committee warned that the plans as they currently stood could be open to a series of legal challenges on human rights grounds.

And ministers were warned that  re-introducing means testing for defendants could lead to delays in the criminal justice system.

But there was agreement with the government that the "spiralling criminal legal aid costs" needed to be tackled.

"There is no doubt that the government is right to look for ways to restrain the criminal legal aid budget," said committee chairman Alan Beith.

"Since 1997 it has spiralled out of control, squeezing the amount of support available for other important legally-aided work.

"Clearly those who can afford to pay for their own legal costs should be made to do so and, in the interests of justice, those who can't should be supported."

Over half of the Department for Constitutional Affairs' budget of £2 billion is spend on criminal legal aid, a situation which the draft Criminal Defence Service Bill aims to tackle.

However, the report warned that the government had not produced any convincing evidence that re-introducing means testing would lead to substantial cost savings.

"Two of the proposed means testing models would be unworkable in practice and the other may lead to successful challenges under the Human Rights Act," warned Beith.

"This will inevitably lead to delay and more costs, the exact opposite of what the government says it wants to achieve.

"The problem is partly due to initiatives pursued by a range of government departments which have resulted in more prosecutions and therefore more demand for criminal legal aid."

Instead, the committee said there should be a greater focus on reducing expenditure on the handful of most expensive criminal cases which consume a disproportionate amount of the Criminal Defence Service budget.

Anecdotal evidence submitted to the committee suggested that the most expensive six cases account for a quarter of the entire Crown Court legal aid budget.