A woman walking her dog near the river on Friday evening said she saw a red rescue boat on the water at around 10:00 BST and that there was a helicopter nearby at the same time.

The woman, who wished to remain anonymous, said: “We could see they were searching in the water, they had walkie-talkies, we could tell they were searching for something.”

The Environment Agency had issued a “red warning: strong current” warning for the section of the Thames between Shepperton Locks and Molesey on Friday morning.

Efforts are underway to determine how the boat capsized.