We had this question a couple of days ago, and a full answer was given. (Of course I can't find that question!)
As I remember, its a North East London exchange on NTL
A bit of Googling on the code shows taht it covers places like Ilford
It is certainly Ilford. Look at the phone number of this business address: -
Computer-Tech Screens
South Park Business Centre
310 Green Lane
Ilford
IG1 1XT
Essex
Tel: 020 8924 1494
Fax: 020 8597 5901
As it's not a BT exchange, it covers a wider area than you might expect.
When the question was first asked, I spent far too much time looking at addresses which were thrown up by a Google search on the code.