I just discovered that it is the adaptor that is at fault. Change the adaptor and renew all the rechargeable batteries and you will probably have the equivalent of a brand new system!! BT are not particularly helpful because when you call the number in the manual, it directs you to another number which then gives you options (as usual!). You then select the option for ordering accessories and it then directs you to yet another number for technical support which is chargeable at over £1 per minute!!! - if you're outside the warranty. The BT shop does not sell this adaptor; they say it is no longer sold. They give you alternative suppliers who are perplexed and annoyed that their number is being given out as they simply don't sell accessories for BT.
The best thing is to try and source the adaptor from an electronics store (maybe a compatible one) or try ebay for a second hand one. Hope this helps.
techman
January 2009