On a windy hill in Scarborough, next to a slightly ramshackle sheep farm, one of Britain’s most secret buildings sits behind a barbed-wire fence. It is a GCHQ base dating from the First World War, when our spies intercepted messages to and from the German fleet. More recently it spearheaded an investigation into Manchester bomber Salman Abedi’s terror network.

The Sunday Times has been given exclusive access to the base as GCHQ today announces a significant expansion of its northern spy hub. It is recruiting 100 extra personnel to counter the threat from domestic terror and Russia.

A web of tall, thin antennae can be seen rising out of the surrounding fields as we drive to the base along a narrow road. We are greeted