London does a brisk tourist trade year-round, but July and August are the busiest months, thanks to the warm weather and school holidays; many hotels offer summer specials.
Off Season: October to March
Weather is unpredictable, with grey skies and rain a distinct possibility, but crowds thin somewhat, and theater/art shows provide plentiful indoor entertainment; just don't expect room rates to dip dramatically.
Sweet Spot: October; April
Visit right after the school break and before the Easter holidays to dodge the masses, find good deals, and maybe even catch some stray sunbeams.
