no, call the number listed - it's a national number that works no matter who your supplier is (as your supplier doesn't actually have anything to do with the supply to the house apart from billing you).
[edit]
Also if you haven't done so already, head towards the cupboard/room where the gas supply enters your house, pull the lever marked "gas" into the off position, thus cutting off the supply at point of entry to the house.
Once the gas man arrives he'll turn it back on and do some tests - if he finds a problem he won't fix it (if it's an appliance at fault), but will note were it is at which point you call in you friendly neighbourhood corgi registered gas engineer/plumber to fix the problem (at this point having cover with the likes of British gas comes in very handy as you then don't pay for the repair).