Sure enough he turned up and got to work on my master socket. He had no issues using a high quality RJ11 cable and a power jack extension I already had, and once it was up and running showed me I'm getting the full 80/20 speed
My wireless g devices have no chance, but wired devices are getting 75/19 so I can't argue with that. Just got to run some Cat5 to a switch upstairs so I can take full advantage in the rest of the house.
I did notice I've got an ECI modem and what looks like a Huawei cabinet (only discovered about the differences after the engineer was gone!) . Might buy a cheap Huawei modem in the future and fiddle around but everything seems fine so far.