The insurer of the Yarl's Wood detention centre, which was wrecked by fire two weeks ago, has provisionally estimated the damage at £43m - £5m more than originally thought.

The insurer of Group 4, which ran the centre, is Lloyd's Syndicate DJ Pye 962. Active underwriter David Pye stressed that because loss adjusters had not yet been allowed to investigate the site, there was still uncertainty over the final figure.

But he said reports indicated a riot took place, as defined by the Riot (Damages) Act of 1886.

"We underwrote it [the centre] on the basis that riot damage would be principally recovered from the police authority ... we would expect to recover the main property damage under the Act," he said.

He added that he doubted whether riot cover would be available for other detention centres if access to the Act was denied.

Pye said the policy on the Yarl's Wood centre was up for renewal at the end of March and that it would be reviewed in light of such a serious loss.

The three joint policyholders are Group 4, the centre operators, Amey, the centre contractors who built it, and the Home Office.