Securicor, the UK-based security group, may have to write off �35m as it runs down its US airport security business ahead of nationalisation.

The news came as Securicor reported profits before tax rising to �63.8m for the year to September, up from �54.9m last year.

Sales for the firm, which has security interests in the UK, the US, Canada and across Europe and Asia, rose 58% to �1.14bn after a series of acquisitions in the US, UK, Holland and South Africa.

The company's US subsidiary, Argenbright, with turnover of �120m, will have to be out of the business within a year.

Argenbright has had its licence to operate at Boston's Logan Airport taken away after a series of security breaches.

Logan was one of the airports from which the passenger jets hijacked on 11 September took off.

But Securicor said it believed its operations were "properly carried out in accordance with contractual requirements".