Moving existing phone number to new line

[#1]

I've just got a 2nd PSTN line installed in my house with BT providing the line and using Plusnet as the Broadband supplier. I did this because the existing line has very poor transmission and only runs at about 500kb/sec. The new line runs at about 1.5mb/sec, which is what I would expect given the distance from the exchange which is about 3 miles.
I intend to cease the old line and broadband service with BT/Virginmedia but my problem is that I would like to transfer the phone number from my old line to the new one. Is there any way that I can do this?  I need to be very sure that BT don't simply give me back the old crappy line when this is done.
Derek

[#2]

You probably can transfer the number over, although if both lines are with BT you'd be best posing this question to them.