I've had several unanswered calls from 0800 064 1087. Today I answered it, it was a bloke saying he was calling from 02 (my mobile service provider) and asking me to confirm my name and other details. I told him to clear off as I never provide these to cold callers.
I checked it on whocallsme and it's not 02 at all:
http://whocallsme.com/Phone-Number.aspx/08000641087
I have reported it to 02 who confirm that they never ask people for details if they ring up (not that they ever have). I hope this might help someone else!