There is one exception in the U.K to the rule that traffic must drive on the left. This street is found in London and is called Savoy Street and is just off the Strand.
The reason for the exception to the rule is due to the Savoy Hotel at the end of Savoy Street. The hotel is grand and expensive and therefore mainly attracts people with large bank accounts. These people prefer to turn up in style to the hotel and so often arrive in limousines. However the problem arises when the limousines need to take the left from the Strand to the hotel.
Due to the large turning circle of limousines and the comparatively small width of the street many drivers find themselves on the right side of the road after finishing the turn. The danger of oncoming traffic ensues. So city planners seeing that the Savoy Hotel's entrance was also on the right side of the street decided to make the street the only one in the U.K where traffic drives on the right.
The road leads to the hotel and is not a through-road so drivers once arriving at the hotel simply perform a U-turn (whilst staying on the right) and drive to the end of the street where there are traffic lights to regulate the system.