I took the Maplin adapter apart and was suprised to see that it connected:
BT plug 2 to RJ45 5
BT plug 3 to RJ45 7
BT plug 4 to RJ45 2
BT plug 5 to RJ45 4
Following the route with my T568B-B patch lead, this means that 'phone (BT) plug 2 goes into the BT socket where BT plug 5 would go if plugging in a phone directly (sorry about the clumsy description but I think BT sockets are numbered differently so didn't want to confuse everything), 'phone plug 3 does not reach the BT socket (explains no ringing), 'phone 4 goes into socket at BT plug pos 3, and 'phone 5 goes into the socket where 2 would go.
I've tried making a patch lead that maintains the positions so that BT plug 2, 3, 4, and 5 end up going into the socket where it would do if you plugged the phone in directly but didn't even get a ring tone from that one.
I've also tried putting an RJ45 plug on an old 'phone cable directly a couple of times without getting it to ring, one maintaining the pins order and one reversing them, but still can't get the phone to ring.
I am out of BT plugs now (!) but the one thing I can see left to try is to make up a patch lead to connect Patch Panel 7 to BT 4 and try the Maplin adapter again. However, as far as I can see, this would be the same as when I put the RJ45 straight onto the old phone lead with pin order reversed.