You're right in that pub food tends to be cheaper than "restaurant food" - but what makes the UK so expensive these days is the exchange rate. When I was living there (1989-90) the exchange rate was $1.85 to the £ and most price tags I saw used the same numbers as in the States, only with the £ instead of the $.

Lately the exchange rate has been pretty much the same - and the Tube fare is now up to £4 a ride. (Compare that to $2 or so in the NYC subway.)

But to some extent it's kind of misleading to compare individual items at current exchange rates. You spend your money on such different things - national insurance instead of medical insurance (and co-pays and deductibles), and you adjust your food budget to buy what's available (fish & chips vs. McDonalds or a pub lunch vs. Panera Bread). If you're living on a US$ denominated salary, then the converted costs are relevant, but if you're living on a local payroll, you just think in terms of how much of your salary goes to each category without the exchange considerations.
Cheers,
Bev