I did a search on the plug before posting and thought it was RJ11, I thought RJ45 were computer network plugs? Anyway it is the plug that is normally on any standard phone cord that plugs into the phone end.
I was trying to keep my post simple, and negelected to mention I've just recently done exactly what you've suggested in your third paragraph Cryril, and yes you're right that is the setup - with a Krone block in a cupboard which I rewired to have a proper splitter inserted and have the phone sockets coming off one side and on the other side with the main line splitting off to the computer socket. Unfortunately that line also connects out to the Sky so I have to have a Filter on it as well, thus some of the messiness.
I also installed a double BT face plate from DSE to an existing flush mount but it just looks too cheap. But I can't do that to all of them anyway as some of them are combo Phone/Aerial plates. I've looked and never been able to find an RJ11 ADSL filter. Yes I would like a patch panel but can't justify that as I won't be making frequent enough changes. Maybe one day when moving to VOIP.
It's not a big deal, just wanted to finish tidying things up if it was easy to do, Keen to know where a person off the street (ie: not a professional installer) can go to get a better selection of stuff than you can get from DSE etc.