MPs have reacted with anger at plans to allow evidence of a defendant's previous convictions to be more readily admissible in court.

The cross-party criticism centred on claims a jury would be more likely to convict someone with previous criminal form and regular offenders - or the "usual suspects" - would be more at risk from conviction.

Speaking in a House of Commons debate, Conservative former Cabinet minister John Gummer warned Home Secretary David Blunkett it was an "extremely dangerous road to go down".

Simon Hughes, the Liberal Democrats home affairs spokesman, called for the new powers to be removed from the Criminal Justice Bill, arguing they could prejudice the right to a fair trial.

The bill, which will overhaul the criminal justice system in England and Wales, includes proposals to restrict the right to trial by jury and would scrap the "double jeopardy" rule that prevents a suspect being tried for the same crime twice.

Bar Council

But Junior Home Office Minister Hilary Benn said that far from undermining the principle of innocence until proven guilty, the bill was trying to address a "haphazard, inconsistent and unpredictable" system.

The outrage came as the Bar Council, representing 14,000 barristers in England and Wales, launched a campaign to stop the government's "objectionable" criminal justice reforms.

The Bar Council opposes three aspects of the bill:

During report stage debate, Mr Hughes argued that the right to a fair trial should not depend "on evidence about large elements of a defendant's previous life", which related "not just to previous criminal convictions, but much wider matters".

His party wanted to start with the presumption that no bad character evidence was admissible, he said.

"People who have had form, committed offences, been tried and convicted but who have gone straight and are trying to rebuild their lives, become much more at risk of being brought back, tried, convicted and wrongfully convicted," he said.

'Dodgy evidence'

Labour's Vera Baird, a QC, described the plans as "extremely dangerous".

"You will put people who this government says it wants to rehabilitate... in a position where they are trapped in their past and they cannot get away from their past," she said.

Labour's Chris Mullin, chairman of the House of Commons home affairs select committee, called the plans a "recipe for mistakes", with sex offenders particularly at risk from wrongful conviction.

"A bit of dodgy ID evidence, a cell confession, you add to that bad character, Bob's your uncle you've got a conviction," he said.

Shadow home secretary Oliver Letwin said safeguards were needed to ensure judges considered fully the implications of allowing bad character evidence.

'Important principle'

"It is the most important feature of our whole constitutional arrangements and the most important feature of people's sense of justice in this country that we operate from the presumption of innocence," he said.

"I do not think there is any more important principle in Britain."

Tory Edward Garnier, a QC who sits as a Crown Court Recorder, argued that judges "do not enjoy being criticised later for applying these badly-drafted and ill-thought out laws which we in Parliament impose on them".

But Mr Benn insisted that this part of the bill was not about "rounding up the usual suspects".

"It is not about trying to prejudice juries, it is not about trying to damage the rehabilitation of offenders, it is not about undermining the principle of innocence until proven guilty, it is not about the prosecution no longer having to prove their case beyond reasonable doubt," he said.

"What it is about is trying to get the balance right."

Mr Benn highlighted two recent cases that proved the need for reform.

'Insult'

In one, the jury did not know about the previous form of a man accused of stabbing to death a woman 81 times. He had convictions for using a knife and for beating people.

In another, a woman who claimed she was raped by a doctor was not allowed to give the proper circumstances of her story because it would have involved revealing the doctor's convictions for sexually assaulting nine other patients, he said.

"At the same time, just to add insult to injury, she was cross-examined about a child she had adopted 36 years previously, the taking of a valium tablet and an alleged sterilisation operation," he told MPs.

"On the evidence of those two examples, and there are others, despite the fact that potentially a very wide range of bad character evidence can currently be admitted, it is not the case that those provisions are being applied on a consistent basis."

The debate was adjourned.