£1 less than you currently pay?
I don't think that how long one has been a customer determines what kind of offer you get - more what package you already have from BT, how much you currently pay and whether you are in contract or not.
If they were intelligent, they would also use the maximum speed your line could support in their formula but I suspect they don't do this.
You could always try calling BT's customer options team on 0800 800 030 and see what deal they will offer you if you say you are thinking of leaving due to the price rises due in July though I know many don't like haggling over the phone hence one reason why the link I posted might be useful.
Sadly, I think all companies tend to reserve the very best deals including cashback and free equipment for new customers - partly to get market share/as a loss leader and partly as they hope you won't move afterwards.
Still its interesting to hear about what others are offered..