>>> "It does say hello initial and surname".
Well done on looking out for one of the tell-tale signs of scams. (i.e. anything that starts "Dear Customer' is likely to be very dodgy). However if, say, your email address is
[email protected] (or something like
[email protected]) it's not exactly rocket science for a scammer (or the software that they're using) to work out that you're 'J Simpson'.
It's a classic scam. (Scammers like to rush people into doing things by announcing very short deadlines before something nasty will happen).
However, if you still want to check, examine the full headers for the email. The way to do so varies depending upon how you receive your emails but if you're using BT's webmail service, open the email and then go to the Menu to select View > Message > Raw Source. That will show the real email address that the email came from. It'll probably be a Gmail one, or similar, and it seems safe to bet that BT won't be using Gmail!