Home Secretary Jack Straw will announce plans to change the law to allow a dramatic increase in police use of DNA and fingerprint evidence

The BBC's Jane Peel: "Keeping DNA samples will save time, money and inconvenience"

A Home Office consulation paper says the DNA profiles should be held on a database if those involved agree.

The government says this will save time, money and inconvenience.

The BBC's home affairs correspondent Jane Peel says DNA profiling is increasingly being used to catch criminals.

'Caught by dandruff'

Advances in technology have enabled police forensic scientists to make a DNA match on evidence as small as a single hair or a piece of dandruff.

In the past only blood would suffice.

DNA tests have been particularly successful in cases where police have had to test hundreds or even thousands of people.

But under current legislation, the tests have to be destroyed if someone is caught and convicted.

The BBC's Jane Peel: "There would need to be safeguards"

There have been 120 mass screenings in England and Wales, gathering an average of 4,000 samples at a cost of £40 each.

The increasing use of mass screenings meant some people were being approached more than once.

Not only is this a waste of money, but it has sparked fears that people will refuse to give samples on the grounds of duplication.

Mr Straw said the samples would only be stored with the donor's consent, and would be kept on a separate database to the National DNA Database. This contains samples from 600,000 offenders.

At the moment, around 600 matches a week are made on the database, which is the biggest in the world.