As many as 90 Afghan nationals are being detained in a holding facility at Camp Bastion, the Defence Secretary has admitted.

But Philip Hammond denied the men were being held illegally, as lawyers have claimed.

Responding to accusations that the facility had been kept secret from the British public, Mr Hammond said: "I'm not going to comment on individual cases. What I will say is that the assertion that this is a secret facility is patently ridiculous."

Mr Hammond put the figure for the total number of men held "in the high tens, around 80, 90".

He said parliamentary archives showed that the Government had been transparent about the facility.

Legal documents obtained by the BBC indicated that dozens of suspected insurgents are being held at the base, in what their lawyers claim could amount to unlawful detention and internment. They have also been critical at the lack of access they have had to their clients.

Phil Shiner of Public Interest Lawyers said the Ministry of Defence had refused them access to their clients and only as a result of legal proceedings had they managed to establish telephone contact.

He said the Government was failing to deal with the suspects "humanely" and according to international law.

"What happens is the UK could have trained the Afghan authorities to detain people lawfully with proper standards and making sure that they are treated humanely. They could have then monitored that, including with ad hoc inspections to make sure that the Afghans were obeying the law. They have chosen not to do so," he said.

Mr Hammond dismissed the claims, suggesting the lawyers' requests would pose a threat to British troops.

"Let's be clear what they are asking for: they are asking the court to release these people to turn them back to the battlefield so they can carry on with the activities for which they were detained in the first place," Mr Hammond said.

He added that the legal proceedings were "at the expense, of course, of the British taxpayer, because Mr Shiner's actions are funded by the legal aid system".