you mis understand. I realise the copper pair will stay in the ground but when will the service via that be removed now that digital voice is up and running. i assume the connection in the exchange will be removed at some stage
Do you mean, you still have dialtone on it? If so, you can dial 17070 to find what phone number is currently assigned to it.
Again, they won't disconnect it from the exchange unless they run out of ports there (which is very unlikely), because you could always request service to be reactivated at any time.
What's more likely is that if there's a fault on someone else's line, they might switch them to an unused pair, and *that* could disconnect you.