House move and LLU question

Hi All

I am (thankfully) currently on an exchange with no LLU providers but we are planning to move house next year. So, if the exchange we end up with has LLU can I specify when I ask for the ADSL move to be kept on the BT system? Or do PlusNet (or any ISP) simply 'connect' you to the system they see fit?

I hope that makes sense and that someone can throw some light on this matter.

TIA

Only thing I have seen was that with a new signup the option to opt out of LLU appears part way through the ordering process