Lord Brian Mackenzie, a Labour peer and former head of the Police Superintendents' Association, and Bruce Holder QC, chairman of the Criminal Bar Association, give their views.

Lord Brian Mackenzie

The question of using previous conduct or convictions as evidence of guilt is contentious.

It cannot be denied that as a tool of investigation, the proposition that a person's previous pattern of conduct is an indicator of future activity cannot be denied.

The law at present allows evidence of 'similar facts' to be adduced where the modus operandi is so similar that it shows a systematic course of conduct.

In my experience of 35 years as a police officer, judges are very reluctant to allow such evidence because its prejudicial effect outweighs its probative value.

The law must safeguard the innocent but it also has a duty to convict the guilty

Lord Brian Mackenzie

I think this should be reviewed and perhaps allowed in more often in the public interest.

Similarly, if the defence attack the character of prosecution witnesses, evidence can be led of the accused's character, to show his dishonesty. Again it is a rare occurrence.

If a man has been acquitted seven times for date rape of girls he met in pubs, that is very relevant when he runs the same defence of consent and in my view should be admissible.

Similarly, I know of a car thief whose fingerprints were found on the inside mirror in each of three cars he was alleged to have stolen.

He demanded separate trials and in each case he ran the defence that he had been picked up as a hitch-hiker and therefore had lawful access to the car. He was acquitted on each occasion.

The law must safeguard the innocent but it also has a duty to convict the guilty - miscarriages work both ways and in my view, there is room for improvement.

Bruce Holder QC

A trial is about discovering whether a person committed a particular crime.

A fair trial is not one based on prejudice.

To prove a person's previous convictions usually says nothing about the crime a court is considering.

Those who call for convictions to be admitted often ignore, or are unaware, of the fact that previous convictions can be relevant, and are already often admitted in evidence.

When the circumstances of previous offending are so similar as make them relevant, then the law and judges, do permit the evidence to be admitted.

Proof should not be substituted by prejudice

Bruce Holder QC

For example, a rapist who always wears a particular unusual item of clothing, or uses an unusual method to subdue his victim may find his past crimes proved in proof of a crime where the same methods were employed.

The test is not whether a person has a propensity to rape, burgle, or stalk, but whether he can be shown to follow an unusual and personal pattern in his offending.

Also, a person of bad character who pretends to be of good character, or a defendant who accuses a prosecution witness of lying, will often find his own convictions admitted in evidence.

The law has recently even allowed the facts of previous acquittals in previous trials of rape where each time the facts were similar and each time the defence was the same - this was because it was relevant.

In short, people should be brought to trial on real evidence, and proof should not be substituted by prejudice.