Where Is The Most Haunted Pub In Britain?

It's a bit of a subjective judgement, but The Ostrich in Colnbrook usually gets nominated.

It's a very old pub, argued to be the third oldest still-running pub in England.  Among its many prestigious guests: King John (who signed the Magna Carta, Queen Elizabeth I and possibly Dick Turpin (the highway bandit).

The haunting didn't come about because of the famous visitors.  But rather the habits of one set of landlords: Thomas Jarman and his wife in the 17th century.  The wicked couple had rigged up an ingenous death trap in a room just above the kitchen.  Basically, rich guests who laid down to bed in there would find their beds tipped vertically and themselves thrown into a vat of boiling water.  The body would be thrown into a nearby river and the victim's things sold for profit.  

The Jarmans were only found out when the horse of one of their guests escaped unexpectedly and was recognised.