Here's the low-down:
Lager , the most widely-consumed beer in the world, is served cold. This inlcudes Budweiser, Coors, Miller, etc. Beer snobs will tell you that lager is served as cold as possible to numb your tastebuds so you dont know it tastes like piss.
Ale, such as Newcastle Brown Ale and stouts are traditionally served at cellar temperature (approx 55 degrees F), however, most I've experienced are served around 40 degrees F, which I would call cool, not cold. Although, I should probably mention that I don't spend much time in real ale pubs, where you are more likely to find cellar temperature ales. If you're after this traditional experience, check out the Campaign for Real Ale. To further complicate the matter, Guinness, which is a stout of course, now offers "Guinness extra cold", which is available on draught and is apparently very popular (says my local publican).
Beer is not served warm in England.