In reply to ablackett:
I seem to remember an episode of QI mentioning that the Isle of Wight was the smallest county in the UK at high tide, but not at low tide when Rutland beats it!
Whether the IoW is a county or not is a whole other question of course, although Wikipedia says this...
"The Isle of Wight is a Ceremonial and Administrative county and as it has no district councils (only the county council) it is effectively a Unitary county, though not officially. It is unique in England in this way - all other Unitary areas are single districts with no county council, while the Isle of Wight is the other way round. It also has a single Member of Parliament, and is by far the most populous constituency in the UK (more than 50% above the average of English constituencies)."