Hi again,
First let me thank you all for the advice.
The point about the ip address may be beyond my abilities, but I'll keep it in mind for my sons to try maybe.
The Powerline adapters are BT's own, one piece of advice I was given by a BT engineer was to plug the adapters into a double socket and press the re set button until they 'spoke' to each other, this didn't always work. I haven't tried switching them off and on yet, but my last point may cover this.
How often? at first maybe a week or more, but recently I have had to re set twice a day on occasion, I usually find the fault in the morning after everything has been ok the previous evening, but not always.
All other devices connect to the internet ok.
Regards,
Peter