Scores of top secret files relating to the administration of the United Kingdom's colonies may have been destroyed.

The Foreign and Commonwealth Office is unable to confirm whether 170 boxes of classified documents which were returned to the UK at the end of the colonial era have been destroyed.

The admission, by Foreign Office Minister David Lidington, came as files relating to controversial British activities in Kenya and Cyprus were opened to the public.

Attempts by UK authorities to cover-up the killings of 11 prisoners during the Mau Mau uprising in Kenya were disclosed in the documents. Detainees at Hola detention camp had been clubbed to death by warders.

Mr Lidington said the documents were the fourth tranche of colonial files to be disclosed, marking the halfway point of the process of transferring the papers to The National Archive.