A TV disaster movie showing London flooded is a "complete fiction", according to the Environment Agency.

In the drama Flood - shown on ITV over the bank holiday weekend - parts of London were engulfed by water.

In the film a storm in the North Sea, combined with Spring Tides, created a surge of water large enough to swamp the Thames Barrier.

But according to experts at the Environment Agency, this could never happen.

A spokesman said: "The film is a complete work of fiction and portrayed as such, but perfect for the small screen.

"The story line is far-fetched, suspending reality.

"It is very dramatic and over the top - as disaster movies are designed to be.

"The film is not based on fact. Recent modelling that the extreme conditions you would need to overtop the Barrier would in reality not occur.

"It is true that London is at risk of flooding but a flood like this could not happen."

According to experts, the Thames Barrier will continue to provide protection until the end of the century - even allowing for the effects of climate change.

Prediction models - which took the most intense wind and pressure fields ever recorded in the North Sea, combined with the highest astronomical tide on record - could not produce a wave to defeat current defences.

Even if a surge took the form of a tsunami, the water would dissipate lower down the Thames Estuary, long before it reached central London.

Typically a surge would involve higher water levels but a tsunami wave could be caused by an external event - for example an earthquake.

The last time this happened was after a landslide off Norway 8,200 years ago and geologists estimate it could be 100,000 years before the next one.

London currently stands a 0.05 per cent risk of flooding in any given year.

As sea levels rise, the level of protection provided existing defences will decline - and by 2030 the risk of flooding will be 0.1 per cent.

An Environmental Agency spokesman said: "This is still a very high standard of protection, but if improvements are not made in the future the defence standard will continue to fall ultimately reaching unacceptable levels of risk."