I hope you don't mind my answering, Jenn, since I'm in the US.
I'm a vegetarian and nearly vegan (I already stopped drinking dairy milk, and because I cook so much for myself and have gotten out of the habit of using dairy, eggs, etc.) I've been this way for about a year - though fish was definitely the last meat to go from my diet since my whole reason for vegetarianism is that I just didn't find meat that appealing and fish was the one meat I could stomach. I was vegetarian for about a year and a half when I was younger but it just wasn't a sustainable thing for me at that time.
Eating dinner with others who are omnivores, they either prepare something suitable for me to eat or I bring something of my own. Now, granted, I'm not talking fancy dinner parties here, just mainly family-style meals where it's not such a big deal if I provide for myself. There's nothing wrong, when invited for dinner, finding a polite way to mention your dietary needs. Vegetarianism isn't so uncommon any more so I feel like it's not such a shock for people to find out that that's how you eat.
I don't know what part of the UK you're in but it's been my understanding that things are pretty good for vegetarians in some areas of the country, as far as dining out and grocery shopping go.
Protein, I don't so much worry about because I know if I'm eating a diverse amount of foods, the protein will be taken care of. I like to make baked tofu dishes, I prepare my own seitan (wheat meat), eat lots of peanut butter and some other "mock meats." From what I've read of your food-related posts, you seem to already be into eating in a healthy manner (not that all vegetarians/vegans DO eat in a healthy manner) so I don't think the transition to veggie would be a big upset for you. You would just learn to plan your meals differently and soon it would just become habit.
If you have trouble with finding foods you like to prepare, I would recommend sites such as Bryanna Clark Grogan's (you should see her Thanksgiving and holiday dinners!) and
VegWeb (great because their are user reviews of a lot of the recipes.)
Lots of luck if you decide that vegetarianism really is for you!
