Campaigners say some children are losing out

The Fostering Network said the country is short of 700 carers and has called on ministers to invest more funding in fostering services.

More than 3,000 children are living with just over 2,000 foster families.

Experts stressed that the severe shortage of carers means many children have to move households several times during their time in care.

The Fostering Network warned the crippling shortage of carers will only begin to be fully tackled when there is proper investment in fostering services.

Local authorities know there is much work to be done, and many are actively developing recruitment and retention strategies Bryan Ritchie The Fostering Network

Scottish spokesman Bryan Ritchie said: "The situation was bad enough in 2002, and this survey shows an alarming rise in the number of carers needed.

"Too many children's lives are being badly disrupted with frequent moves and foster homes a long way from family, friends and school."

Mr Ritchie said the system was not providing these children with the security they need.

He said: "Local authorities know there is much work to be done, and many are actively developing recruitment and retention strategies."

"But the Fostering Network believes this crippling shortage will only begin to be fully tackled when these words are backed up by proper investment in fostering services."

The Scottish Executive has acknowledged the problem and insisted that it is committed to improving support for fosterers.

Campaigners have also demanded the same amount of cash for all foster families, as many currently end up out of pocket.

They have called for carers to be paid as employees rather than volunteers.

One residential school - Kibble, in Paisley - has been offering more than �20,000 per year to try to attract carers from other occupations.

Statistics from the Scottish Executive showed one in four children living away from home in public care lived in three or more homes in the year ending 31 March, 2003.