It's British Gas trying to sell you insurance on your boiler, central heating system etc.  £15 per month, guanranteed to be with you within 4hrs of phone call, even on Christmas Eve.  All sounds reasonable, but what I didn't like and the reason I didn't take it up was that they want you to fill in your bank details over the phone (only sort code and account number, no security details) so that they can fill in the direct debit form and send it out to you - you then have 21 days to decided whether you want to continue, if you don't you then have to cancel the agreement they've already set up.
The chap was pleasant enough but too persistant for my liking.  I suggested they send me all the bumpf and I'd fill it in myself after I'd read all the smallprint etc. but they wouldn't let me do that.