It appears to be a company called Docklands Telecom, see
this thread on MSE. A Google of
Docklands Telecom gives
this page as the first result which dates back to May 2004 and shows how long these people have been creating a telephone nuisance.
A search of
docklands telecom nationwide brings up several results including:
Docklands Telecom Centre Ltd
Unit 9 Ashton Gate
Ashton Road
Romford
Essex
RM3 8UF
For the above address, one entry gives 0870 0424433, which is very similar to the number that the cold calls have been coming from. The address is north-east of Romford and a further search reveals
.
The above address also has the number 020 75382626 by its 192.com listing, which is on Poplar exchange, but doesn't accept incoming calls. This is in central London on the Docklands (see
here for map).
From the results on 192.com, I guess Docklands Telecom's Docklands address must be:
1A BURDETT ROAD
LONDON
E3 4TU