Deadly downpours.

Flash floods usually happen in places which have experienced a long dry spell, baking the ground and making it harder for water to drain away.

Sunday's storms were caused by a weak weather front meeting hot and humid air, which caused instability in the atmosphere.

Lucy Verasamy, of the Press Association WeatherCentre, said: "Once there is an intense, sustained spell of rainwater, it cannot be absorbed by the ground and starts to cause flooding.

"It is especially a factor in places with high ground like Yorkshire, as water running off the ground will begin to flow down to low-lying places."

One of the worst flash floods happened last year in the Cornish village of Boscastle, when 181mm, (more than seven inches), of rain fell in five hours. River levels rose by two metres, (6ft 6ins), in an hour as the area was submerged.

On Sunday the rising flood waters caused drivers to climb trees. A major clean-up operation is under way and the cost is likely to run into tens of millions of pounds after the rain washed away roads.