BT8500 Cordless Phone - Can't Make Or Receive Calls After Power Cut

We have a BT8500 cordless phone which worked fine until we had a power cut yesterday.
Power cuts have happened in the past and the phone has always worked.

I keep getting the following message on the phone "Can't use that feature on this base".
The phone rings when receiving a call, but you can't answer it. So the phone line does work.

Other "normal" phones in the house work OK.

The batteries are fully charged and I've tried other batteries. I've also unplugged everything for 10 minutes.
I think the base and phone just need relinking together, but everything I've tried from an internet search doesn't work

i.e. the Find Handset mentioned here fixya.com/sup…ork

Is there way to fix the problem without resetting the phone and loosing phone numbers, block lists etc?

Thanks for any help.