Some offenders have been sent to English institutions

The study found that places are not being found for dozens of youngsters every year.

More accommodation is to be made available but the Scottish National Party (SNP) is warning that plans will not meet demand.

The party claims there will be a shortage of spare beds if greater use is made of tagging and anti-social behaviour orders for under-16s.

The measures, being proposed by the executive, will be enforced with the threat of detention in secure accommodation.

Any alternative to custody is only going to be effective if the person being tagged knows that there is an ultimate sanction Nicola Sturgeon, SNP justice spokesperson

The new figures show that 71 requests for secure care were not met in the year 2001-02, with some youngsters sent to English institutions.

The executive has promised to increase the number of beds by 29 to 125.

The expansion, to be complete by 2007, is designed to meet existing demand.

But the SNP has branded the plans as "utterly unacceptable".

The party called for secure accommodation to be doubled in the election campaign.

SNP justice spokesperson Nicola Sturgeon said: "Any alternative to custody is only going to be effective if the person being tagged knows that there is an ultimate sanction of being sent to a secure unit.

Junior tagging and anti-social orders are planned

"If that capacity doesn't exist then I don't think tagging is going to be as effective as it might be."

Ms Sturgeon said she doubted if an increase of 29 places would even meet current demand.

She also accused the executive of sneaking out the report by only placing it on its website on the last day of the parliamentary session.

But the executive defended its plans and said the expansion would meet both present and future demand.

"This is not a figure plucked out of thin air," said an executive spokeswoman.

"It was reached following close consultation with the local authorities, who provided us with information on demand in their area."

BBC Scotland's political correspondent Glenn Campbell said the crucial issue was whether tagging and anti-social behaviour orders were direct alternatives to secure accommodation.

"The question of the numbers of places required will depend on how these orders are actually used," he said.