However, the main question is whether the FTTC implementation will have any impact on the speeds for those remaining on their existing broadband set-up?
No. However if your connection is impacted by cross-talk from other ADSL connections it might possibly slightly improve if those connections move to an FTTC service.
Are we effectively moved from a 6km copper link to the exchange to a 1km copper link so even if we remain on the existing basic ADSL we will see an uplift towards 8Mb download speeds?
No. If you stick with ADSL you will still be served by equipment housed in the local exchange. Only those who switch to FTTC will be connected to fibre via the FTTC cabinet that will be located close to your existing PCP cabinet.