Protesters argue that the centre violates human rights

The event was planned to coincide with the second anniversary of the centre's opening.

Organisers the Scottish Trades Unions Congress (STUC) said the protest reflected growing public concern over the treatment of asylum seekers there.

General secretary Bill Spiers demanded that the centre be shut down and that the detainees be looked after in "a civilized and 21st century manner".

The union argues that the holding of children represents an unacceptable violation of human rights.

I think that both the Home Office minister and the Scottish Executive should break the silence on this Michael Connarty MP

Double-decker buses were laid on from George Square in Glasgow to take campaigners to the protest.

Speakers at the event included Mr Speirs and Scottish National Party (SNP) leader John Swinney.

"My concern is that we have a government here responsible for the education, health and welfare of children and they are doing nothing to protect the interests of the children in this centre," said Mr Swinney.

Backbench Labour MSP Elaine Smith has broken ranks with the executive's silence on the issue, which is reserved to Westminster, calling for the locking up of children to stop immediately.

"The treatment of our fellow human beings in Dungavel is every Scot's responsibility - no matter the constitution - and we should all hang our heads in shame for tolerating this aberration in our country for this long," she said.

And Labour MP Michael Connarty also spoke out against both Edinburgh and London's attitudes.

'Normal life'

"I think that both the Home Office minister and the Scottish Executive should break the silence on this," the Falkirk East MP said.

Scottish Socialist leader Tommy Sheridan called the current policy indefensible.

"I think it would be far more preferable that we had individual asylum seekers reporting to a police station on a daily basis rather than this shameful situation," said Mr Sheridan.

The demonstration was supported by the Scottish Refugee Council who condemned the detention of children in particular, claiming the way they are being held breaches international legal standards.

Chief executive Sally Daghlian said: "Do we really want to live in a society where children are unable to lead a normal life, go to school and make friends, simply because of their immigrations status?"

Christian and Muslim groups joined the politicians and asylum groups outside the front gates of the centre.

Those individuals who have got their children in Dungavel have made a personal decision to do so Phil Gallie, Conservative MSP

They shouted slogans and held banners bearing mottos such as "shut down Dunvagel now" and "no to detention".

However, speaking on Newsweek Scotland, Conservative MSP Phil Gallie said refugees were held there for good reasons.

"Those that are in Dungavel, as far as I'm aware, have already been through the immigration assessment process," said Mr Gallie.

"Perhaps in the short term this is something that should be looked at in respect to children.

"But the fact is that those individuals who have got their children in Dungavel have made a personal decision to do so, many have blatantly broken the law and on that basis have put themselves and their children into this situation."

The Scottish Executive has so far refused to comment on the issue saying it is a matter properly reserved to Westminster.

The Home Office said it was unable to confirm how many children were currently at the centre, run by private security firm Premier Detention Services, due to the changing number of applicants.

Campaigners said 22 people under the age of 16 were currently being held.