I've been there a few times, acting as a clerk/legal representative for law firms on behalf of newly arrived asylum seekers. Oakington is probably not the worst detention centre, but even so, the atmosphere there is depressing and the Group 4 guards are prone to severely restricting the movements or freedom even of clerks or interpreters coming in from outside. Once when I wanted to step out of a hut for a breath of fresh air, a guard barred my way and said I could be removed from the site altogether if I didn't go back in the hut. So what they are like with the asylum seekers themselves is anyone's guess.
Locals seemed to be in many cases hostile to the centre even though it probably gives employment to a lot of local people.