I've been wondering this for a while now.
I live in the West Midlands, and when I last went to my GP she said that the closest GIC was either London (Charing Cross?) or Sheffield. Both are a good few hours drive, even London at a 3-hour drive was the closest option. That and I get incredibly stressed and anxious in new places and too close to people, so I'm not a big city person or able (yet) to just jump on a train.
However, when doing a few google searches it seems there is a GIC in Essex. However, I'm not sure why the one in Essex wasn't mentioned in the first place - is it not the same 'standard' as somewhere like London or Sheffield?
I appreciate any information.