The month of June was one of the wettest and dullest starts to summer since records began, the Met Office said.
Despite the temperature being above average for the first month of summer, there were just 138 hours of sun - making it the seventh dullest June since 1929.
It was also the wettest start to summer since 2012, with an average 101.8mm of rain falling across Britain - 39% more than usual.
Data from the Met Office confirmed it was the 11th wettest June since records began in 1910.
Although no counties broke their own records for rainfall, several across Scotland and the South East saw twice the average for amount of rain.
These included Aberdeenshire in Scotland, County Derry in Northern Ireland and Essex, Kent and Middlesex in England.
Despite a sunny start, the end of June saw flash flooding which affected London and the South East, causing some polling stations for the EU referendum to be closed or relocated.
Forecaster Alex Burkill said: "It was generally a wet and dull month with high levels of rainfall in localised areas, and that was to do with the significant thunderstorms and heavy downpours that were experienced in London and the South East.
Burkill said the week ahead would be "mixed", with heavy rain expected in Scotland and the North West towards the weekend and temperatures in the mid to low teens.
In London and the South East, Burkill predicted it would be a little brighter and warmer, with temperatures reaching up to 24C over the weekend.