In the case of your ISP, you will be able to send and receive emails using that address for up to 12 months after you leave them, but you will not be able to manage the address - i.e. change the password. You'll have no access to account management tools.
Thanks for your replies. I don't mind getting a new address and informing people that I know. What concerns me is the likes of banks, sites I buy stuff from, betfair and anywhere really that requires my address a part of its sign in process.
For example what would be the situation on this site if I changed my address, would I have to re-register with a different name (not such a bad idea considering my current one :-) )
Quickbeam, I was with Telewest after Birmingham cable, now Virgin & I still have 2 Blueyonder email accounts active, they are the only ones I have! No need to loose them for me. Personally I find Virgin very easý to deal with.