Hi there Fionnin
I'm technically not in the UK; but am a Brit (from England) who left 5 years ago at about 125kg and then put on more and more. I have had the seatbelt extender nightmare too - I ordered my own off ebay as it was just too embarrassing having to ask for one. I'm now at 109kg and on recent flights dodn't need it - and I could put the tray flat out too
I've joined a gym and am trying the C25K program. Early days but I want to carry on. I use mynetdiary to log calories and exercise and that has been really motivating - I think it is very similar to myfitness pal. I have dropped nearly all carbs, and eat protein with every meal. The carbs I do eat are complex - whole oats and rye bread. And like you, once a week I have a bigger meal, usually at a restaurant here (we have some incredible lunch buffets) - again I limit the carbs but I enjoy the variety in a curry or a Chinese meal. I have also been watching 'Biggest Loser' (some of which I don't like...... such weightloss is not achievable, in my opinion, in ordinary life) and find it great to see real people losing real amounts of weight. The main thing that kicked me off was not recognising Pauline Quirke on tv when watching 'Broadchurch' - i couldn't believe it was her! I then read the book and decided I COULD do it - but using my own diet, not the stuff she used.