Britain had 358.5mm of rain, just beating the 1956 record of 358.4mm.
The main reason for the high rainfall has been the unusually southerly position of the jet stream, a band of strong winds high in the atmosphere.
Following earlier floods in central and southern England, five areas of the country are still on flood alert.
The record rainfall was driven by conditions in England, where the downpour surpassed all other recorded years by a substantial margin.
The record years for Northern Ireland, Scotland and Wales respectively remain 1958, 1985 and 1927.
The figures are preliminary and may be revised at a later date.
Summer of disappointment
"These figures confirm what most people have already been thinking - this summer has been very wet and very disappointing for most," said Keith Groves, the Met Office's head of forecasting.
While it has been wet, the summer has been distinctly average in terms of temperature.
June, July and August saw a mean temperature of 14.1C, almost exactly the average for summers since the 1970s.
The jet stream, a ribbon of very strong winds about 10km up in the atmosphere which brings weather systems to the UK, has been much further south and stronger than usual this summer.
This has brought depressions across many parts of the country.
Environment Agency flood watch warnings are in force for north Devon, Christchurch harbour near Bournemouth, the Mersey estuary, north Norfolk, and the coast between Bristol and Exmoor.
Last Mod: 01 Eylül 2007, 13:34