I'm moving home on 17/05/10, currently living with parents - so I'm not an account holder myself. The place I'm moving to I assume has a BT line. When I move in, it's my intention to get broadband, phone and telly through Virgin.
In terms of BT, with regards to the existing line that (I assume) will already be in place there, what do I need to do - in terms of cancellation etc? as it's not a service I wish to use
It's immaterial who the existing line is with if indeed there is one. These days any time an account is cancelled (assuming it has been) the line first gets stopped then disconnected completely allowing new occupiers the opportunity to get any provider they like to supply services.
Different charges to restart the line though depending on the status.
If there's a dial tone, 17070 will give line number plus test options if it's a BT Wholesale line, should be free to restart by any provider who can be bothered. Only the line number it's not BT Wholesale, may be free to restart, few providers will take you on without hassle and charges for "new line". No dial tone line not active.
If you mean going to Virgin cable then all should have been done by previous occupier regards cancellation.
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It's the responsibility of the current account holder to inform BT that they are moving, and if they have forgotten to tell BT or they are still within the minimum period of a contract, then it's their problem.
That said, if the line is still active, it's probably helpful to phone BT and tell them the old owner has moved out. Just don't say anything to accept any responsibility for the line.