Generally there is a 5 hour difference between these two locations. However, USA and the UK have different daylight savings schedules.
In 2008, during the second half of March and during the first week of November, the time difference will be 4 hours.
(In prior years, the UK started DST one week before the US did, so they were 6 hours ahead for the first week of April. Now the US starts DST two weeks before the UK does.)