The Scotsman understands that Labour ministers are preparing to back police calls for DNA samples taken from innocent people to be retained.

At the moment, Scottish police take DNA samples from anyone who is arrested, but are legally obliged to destroy the samples of people who are later released without charge or not convicted at trial.

In the UK, that legal safeguard is unique to Scotland. Under current rules, anyone arrested in England, Wales or Northern Ireland has their DNA retained regardless of whether they are eventually charged or convicted.

English police forces have used that power to amass a huge database of "innocent" DNA samples. Official figures show that they retain the genetic details of almost 150,000 people with no criminal record.

When the Executive ran a consultation exercise on matching the English rules last year, ministers concluded there was a "clear split" in opinions. While police chiefs strongly backed the plans, civil liberties groups warned retaining the DNA of innocent people could threaten basic rights.

But since the consultation, the police argument has swayed Scottish ministers in favour of greater retention.

Scottish police chiefs have argued that the Scottish exception to the DNA rule should be removed to bring Scotland into line with England.

They also say that retaining all DNA samples could save money, because fulfilling the obligation to monitor cases then delete the samples of innocent people costs more than £500,000 a year.

There has also been indirect pressure for retention from officials in England.

The UK-wide National DNA Database now holds more than three million samples.

The Home Office last month claimed that because English forces had access to the DNA of people previously held but not convicted, they had been able to solve open cases including 88 murders, 45 attempted murders, 116 rapes and 62 sexual offences.

Convinced by such evidence, Labour ministers are now strongly backing the retention plan, although their Liberal Democrat colleagues are resisting.

The Liberal Democrats believe the proposal infringes civil liberties and are worried about the danger to individual human rights of agreeing to such a sweeping new scheme.

At Westminster, Liberal Democrats have been outspoken critics of broader retention.

In Edinburgh, Labour and Liberal Democrat ministers have held a series of discussions to try to find a way through the impasse and it is understood that they are close to a settlement.

Senior Executive sources last night revealed that the Liberal Democrats are likely to sign up to the plan if Labour agrees to introduce new safeguards to defend civil liberties and protect individual rights.

These may take the form of a time bar, forcing the police to destroy DNA samples after a number of years, if the individual is not arrested in connection with any new crime. There may also be strict new rules on the use of DNA samples in future court cases.

An Executive insider said: "There are Labour ministers who are more in favour of this than their Liberal Democrat colleagues. The Liberal Democrats are trying to seek assurances which will allow them to sign up to this."

And he added: "This is an issue which the police feel strongly about and Labour ministers feel strongly about. The Liberal Democrats will want to find a compromise that allows them to support this, because they will not want to be portrayed as being soft on crime."

Scottish police chiefs have continued to argue for wider retention, and a senior police source last night said it was only "practical" to bring Scots rules into line with England.

"From a practical point of view, it would be a bit daft having inconsistency on either side of the Border."

Among the groups that last year opposed broader retention rules in Scotland was Genewatch UK, a scientific lobby group. Sue Mayer, the group's executive director, last night said she was disappointed that the Executive was leaning towards changing the rules. "We had hoped the Scottish Executive would look at this more deeply," she said. "We want a DNA database that works, but there is a better balance to be struck with individual liberties."

She warned that the Executive could face legal challenges over the use of DNA samples which could later be used in scientific research.