UAN-Does it change when you switch providers

Quick question: Does your UAN (Universal Account Number) change when you switch providers? Say you switch from Eircom to UTV and then to Talk Talk does your UAN stay the same?
I want to switch away from talk talk but they are clever enough not to put the UAN on the bill.

You're legally entitled to it, talk to comreg if they won't give it.

I had similar problems with talk talk, luckily I found the number on an old BT bill.

When I called talk talk they want to know why I wanted it. They said we don't have that info to hand and you will need to make a written request for it and that could take 28 days to process.