I too am I the UK. I had post partum thyroiditis and am now hypothyroid (hashimoto's). I was diagnosed in a basic way by my GP. I was sent to the local medical consutant at the hospital who had an interest in endocrine problems.
As it was it worked out well as he is very open to suggestion and takes my worries seriously. However, If I wasn't so insistent about where I wanted my levels to be (from my research) I would have a rougher deal I am sure.
So my advice to you, as we do not have many thyroid experts here, unless you are in a big city, is to get a referral to the hospital to the consultants with an interest and see how that goes, if you do not get along for some reason with him/her, ask to be transferred to another.
I am now almost 26 weeks pregnant too, so I am now seeing an ob and a medical consultant who happens to do the clinic for women with 'problems' again it is working out well, for now, but I am still the one doing the pushing.
I hope that this helps and so sorry for the length!