A secret interrogation centre in Pakistan where British terrorism suspects are alleged to have been tortured after UK authorities had them arrested has been found by the Guardian.

The centre, run by the country's Inter-Services Intelligence agency (ISI), is in the Saddar district of Rawalpindi. It is surrounded by high walls and watchtowers, and bristling with surveillance cameras.

So notorious is the ISI that local photographers are reluctant to take pictures of the centre, although satellite images are readily available...