Got there in the end. The first blood test wasn't used because it was too late getting to the lab (Christmas post I think). So I went for another one and got my license a couple of weeks after that (mid-Jan). It's valid for a year so have to apply again at the back end of this year but really don't care - just happy to back on the road.
The one thing I would say to people is to keep ringing the DVLA for an update because the letters seem to arrive pretty consistently 8 days after they are dated. If I hadn't of phoned them and acted on what they told me over the phone instead of waiting for letters I would still be sitting here without a license.
The lack of liver function tests from my GP seemed in my case to be a non-issue.