A giant thumbs-up has become the 11th sculpture to feature on Trafalgar Square's fourth plinth.

The seven-metre black statue, which features a fist sticking up an elongated thumb, was unveiled on Thursday morning by London mayor Sadiq Khan and its creator, British artist David Shrigley.

Simply named Really Good, the mayor also described the piece as "really good".

Adding that it was the first piece of public art he had unveiled so far in his role as the city's mayor, he joked: "I am 5ft 6(in), so of course we wanted to find the tallest piece of art - and the tallest artist - we could."

He said the sculpture's positive gesture of a thumbs-up would help bring a sense of positivity to the city, particularly in the wake of the EU referendum result.

"I am an optimist, but we have to recognise there has been some doom and gloom after Brexit, so this speaks to everyone."

But Mr Shrigley, from Brighton, was less certain about the message his piece delivers.

He said: "I first said it was a piece to make the world a better place, which in a way is a ridiculous proposition because art is an inanimate object, it can't change the world. Originally it was an ironic statement, but when I come to analyse it, you've got to imagine that your work will make the world a better place.

"It's a very ambiguous work of art because with just that general gesture of approval you're invited to imagine what it's approving of - is it an approval to change things or is it an endorsement of the status quo? The debate that surrounds it will inform what the work is.

"I like the fact that the mayor has decided it's an optimistic thing, so I guess that's what it is, because the mayor said so. People will project their own meaning onto it, but I jokingly say to people 'It means everything - but it doesn't mean that'."

But the artist, also the creator of Partick Thistle's mascot, made clear that he did not specifically have Brexit in mind when he developed Really Good.

He said: "It isn't an endorsement of right-wing political views, or probably any political views."