A rare snake spotted in central London has frightened walkers - who feared it had "escaped from the zoo".

Chris Kutler, 59, worried the Aesculapian snake - also known as a rat snake - was missing from London Zoo after he spotted it nearby.

The walker was out for a stroll on the Regents canal towpath when his dog stopped to look at something in the grass.

He was shocked to discover a dark grey snake – which the Chris said was "too big" to be an adder or grass snake.

After calling a friend to help identify it, he was relieved to discover that despite not being native to the UK the animals are not venomous or aggressive.

Chris said the snake he saw was longer than one-metre but they can grow up to two-metres in length and are one of the largest snakes to be found on the continent.

Chris, from London, said: “The dog stopped to look at something and I thought ‘what’s that’ - and it was a snake.

“I thought it might be an adder or grass snake, but it was much too big for that.

“I realised I was next to the zoo and thought maybe it's escaped from the zoo.

“I was quite mesmerised by it but didn’t know if it was poisonous. So I called a friend who knows about this kind of thing who said he thought it was a rat snake.”

London Zoo said the rat snake did not escape from the zoo and lives on the banks of the canal.