Forecasters have confirmed what many suspected: summer 2012 in England and Wales has been the biggest washout for a century. The Met Office said it had been the one of the dullest on record, one of the coolest, and the soggiest since 1912.

As if to illustrate the point, Cumbria was hit by heavy rain and flash flooding on Thursday, , forcing people to leave their homes and causing a train carrying about 100 passengers to derail.

A landslide is thought to have caused the derailment of the two-carriage train, which was travelling towards Sellafield nuclear plant. No injuries were reported.

While the month is not quite over, Met Office figures up to 29 August make grim reading. Not only has this summer experienced just 399 hours of sunshine, it has also been cool, with a mean temperature of 14C (57F), some 0.4C below the long term average.

The Met Office does not expect summer rainfall (currently at 366.8mm) to exceed the 384.4mm seen in the summer of 1912, and Scotland has escaped relatively lightly with 357mm.

This will come as cold comfort to millions of Britons who have endured the damp weather. It is shaping up to be the fourth wettest summer since records began in 1727.

Torrential rain on Wednesday night forced people in Cumbria from their homes and about 20 elderly men and women were moved to an emergency shelter at Egremont market hall after a power cut.

Egremont and the Calder valley were the worst affected parts of west Cumbria, with 15mm of rain recorded in just 15 minutes at Calder Hall, and a total of 52mm recorded between 10pm and 4am on Thursday.

Passengers on the derailed train were on their way to work at Sellafield when it ran into the landslip at 6.45am. Despite the large amount of mud and debris on the tracks, the train stayed upright.

Alan Isles was on board. He described how fellow travellers screamed out as the train hit the landslide, sending debris flying over the carriages.

Isles, from Workington, said: “As we were coming round a corner, there was no deceleration at all and we suddenly felt a large impact. A lot of people screamed out as the train derailed and many were disorientated. We were worried about rolling over, but luckily we didn’t. The staff were great and took control straight away.”

A second train sent to the scene to transport the stranded passengers to Sellafield also encountered a landslide and had to return to Nethertown. Passengers were escorted to the nearest road for their onward journey.

Network Rail said the derailment, about a mile south of St Bees station, happened in a remote area with no easy road access. Engineers spent the day removing rubble and carrying out repairs. There will be an investigation by the Rail Accident Investigation Branch.

Following the severe weather, Cumbria fire service said it received more than 100 calls for help, mainly involving requests for sandbags. A spokesman said: “Some people have had to be evacuated and many have made their own way out of their flooded houses.”

Cumbria police said drains were unable to cope after the river Ehen and several becks in the Egremont area burst their banks.

Emma Jane Taylor said floodwater began entering her St Bees home shortly before midnight on Wednesday. “We’ve had heavy rain here before, but it’s never been this bad. I alerted some neighbours, but within 30 minutes it was through my front door and coming up through my floorboards. At the moment you can paddle across my floor.”

Earlier this week the rear of a four-storey house in Egremont collapsed into the river Ehen after heavy rain.

Forecasters say Friday will bring largely dry and fine weather for England and Wales, turning cloudier in the north and west later.