Nothing under Basic Boat that I could find as they appear to have been using the 0870 for past few years.
Basic Boat is, however, a trading name of
Howe Maxted Group Limited (their website is currently down!)
A 192.com search of Howe Maxted Group reveals a geographical of 020 8309 1717.
A further check reveals they generally use numbers beginning 020 8309 xxxx so if the above number doesn't help then try a few numbers from 020 8309
1717 to 020 8309
4xxx range.
Let us know how you get on.