According to Yahoo News, there are lots of factors to consider when splitting the bill. It’s like a socioeconomic minefield, but on a small silver plate:
http://uk.finance.yahoo.com/news/How-split-restaurant-bill-yahoofinanceuk-14224902.html
My favourite part of the article is the bit on what to do when eating out on a date. Classy.
What’s your preferred method of splitting the bill? Let me know in the comments.
TPG
The Picky Glutton 
I prefer an equal split but it never happens. If the waiter did separate bills for each person it might take 10 minutes longer for him/her but it’d get us out of the restaurant a good half hour quicker.
My friends and I usually go for an even split, though if it’s obvious that alcohol or meat was a disproportionately large part of the bill, and we have non-drinkers or vegetarians among us, we might work out the initial split without the expensive item and then split the cost of that between the people who had it. So for example on my last dim sum outing, we ordered an expensive roasted meat dish to share among the meat-eaters, and ended up with vegetarians paying £16/head and everyone else paying £19/head (we got the accountant in the party to do the sums!) If one of my friends is a bit skint, we’ll go somewhere cheaper and/or I’ll cover their share of the bill.
Credit card roulette.