Cheers. That's good enough for me. It means that there's no way for RF interference to get back into the ADSL signal if the signal is filtered before or at the same time as it is split - unlike the plugin filters where the signal is split
before it is filtered. (Yes, I know, it's pretty bleedin' obvious, but I just wanted to be 100% sure!)
It's still a pity that there's no getting away from the fact that having the router coming off the master socket is what improves ADSL2+ however it is filtered. In my case, I've just disconnected the phone extension lines as I don't have a filtering faceplate.

ADSL speeds are good and anyway I have a DECT phone with about a zillion extensions so the extension wiring's not needed.

Hmmm... I might buy a filtering faceplate anyway because I just know that I'm dopey enough to plug in something to one of the phone extensions in a year's time and wonder why on earth it's not working.