Staff at London's only secure children's home were last night occupying the centre after resisting attempts to close it for good.

Care workers, managers and teachers at Orchard Lodge in Anerley, south London, took the action after being dismissed and being given less than two hours to collect their belongings and leave.

About 45 employees occupied every room on the six-and-half acre site, including boys' dormitories and bathrooms, to prevent security officers from bolting shut the doors and windows.

The home has been earmarked for closure since March after the Youth Justice Board said it was cutting the number of beds at secure children's units in England and Wales.

But a legal attempt to keep it open was launched by the Glen Care Group – the private firm which bought the lodge from Southwark council in March 2006 but that apparently failed. At 3.30pm yesterday staff were summoned to a meeting and told they were dismissed and to leave the site by 5pm, a Unison official said.

Most of the boys at the 24-bed home have been relocated. But one remaining child was escorted away "in great distress" yesterday afternoon, staff said.

Senior care worker Paul Raythorne told the Guardian the teenager had been looking forward to a parole hearing in two weeks' time. "He was bundled out in a flash and was clearly very upset. He was on a manslaughter charge and like many of the children who were here, he was extremely vulnerable," said Raythorne.

Raythorne said staff had been hopeful the centre would remain open after being told that the legal challenge was going well.

But he said: "All of a sudden our manager was summoned into a meeting by the owners and told that we were all dismissed.

"We have not been given anything in writing. One of the owners and a couple of security guards came down and were trying to screw and bolt the doors closed but we have been forced to occupy the building."

Raythorne said he and his colleagues were prepared to face a police stand-off if necessary and were planning to stay overnight.

He said he understood many of the boys who had been moved to less specialised units had since been subjected to violence.

Orchard and other children's homes are different to units such as young offender institutions and secure training centres because they give more intensive care and have ratios of staff to children.

No child has ever died in a secure children's home, but there have been 30 deaths in YOIs and STCs since 1990.

Daniel Peppiatt, regional representative for Unison, said attempts to dismiss the staff were "unlawful".

"This is an example of the worst possible practice. The staff are enraged. Glen Care have failed spectacularly to consult with their staff."

A Glen Care spokesman refused to comment. The 13 other secure children's homes around the country belong to local authorities.