I know quite a few of you have been to London. You might have seen the Houses of Parliament, St Paul's Cathedral, maybe Hyde Park, maybe Trafalgar Square. What you probably didn't see is the mighty Thames Barrier protecting this busy city. It took nearly ten years to build and was opened in the early 80s.

In 1953 there was a massive tidal surge in the North Sea that hit land over night. 307 people died across the UK. In the Netherlands 1,836 people were killed. There were hundreds more killed at sea. This terrible natural disaster was the precursor for government reviews and reports, leading to a strengthening to sea defences. In NL they built the world's largest movable flood barrier and in London the second largest was built. That is the Thames Barrier.

When you get that far out of the main city and the river is so huge, it's staggering to catch sight of the huge floor barrier across the river.

Visualisation of the damage the highest tidal surge in 60 years could have caused

When it was built, there was a lot of controversy about cost, about being useful. People said the 1953 flood, which crept up in the night and inundated people's homes while they slept, was a once off, that there would never be another like it. But the plan went ahead and it was built. It has been closed over a hundred times n the last 30-odd years for various tidal surges and events - each closure apparently costs £16,000!

Last week there was a severe storm in the North Sea with a major tidal surge. It turned out to be the biggest tidal surge since the one in 1953, so they of course closed the Thames Barrier.

Now, the Environment Agency has released this depiction how much of the city would have been under water, had it not been for the Barrier.

Visualisation of the damage the highest tidal surge in 60 years could have caused

Scary!