While it's a Colchester code, the calls almost certainly aren't coming from Colchester.
I've just tried the number (from a BT landline) and the number is reported as 'not recognised'. That suggests that it's actually from an overseas call centre which is using technology to trick the caller ID system into sending you a false number.
The 'peeping sound' suggests that it's actually a fax service, which is waiting for your combined phone & fax machine to recognise it as such, before sending you an unsolicited fax. (The fact that you've not actually got a fax machine is irrelevant. Somehow or other your number has been entered onto a fax database).
Regrettably I doubt that there's anything that you can do about it without the direct cooperation of your phone provider but, as has been pointed out, Sky charge for call blocking.
Chris