Changing services

[#1]

My BT annual line rental is due to be renewed on the 12th and I'm looking to change over to plusnet.
If I change my broadband too and then fibre is announced, will I get charged from cancelling an annual contract to switch to fibre (fibre with plusnet)?
TIA

[#2]

no but you will start a new contract and almost certainly lose the remaining discounts unless you are very persuasive

[#3]

For line provider switching there is a mandatory (Ofcom regulated) delay of 14 days from placing the order to completion so best to place that as soon as you can. Broadband is likely to switch a few days later.
Regarding fibre (FTTC), you can get an idea of Openreach's plans by entering your postcode in the Where and When checker here. It can take several months from the exchange being enabled to your local cabinet being enabled for service. The definitive checker for current service availability is the BT one here. That also gives your cabinet number if you are not sure.

[#4]

Thanks guys - I will place the order right away. I'm not sure what discounts I will lose, as they've already been paid for (under the BT Line Rental Saver).

[#5]

I think I got the order of switching the wrong way round. Plusnet will normally transfer broadband first, then when that completes move the line.
The discount Oldjim was referring to would be that which currently applies on the Unlimited products if that is the one you have in mind.