A water quality expert from Birmingham delighted onlookers in Trafalgar Square by taking to the fourth plinth dressed as a lump of faeces.

Oliver Parsons-Baker, 26, has teamed up with international charity WaterAid to raise awareness of the billions of people who are trapped in poverty because they lack safe water and toilets.

He was taking part in the art project which is allowing thousands of people to take centre stage in the Square.

The artwork, by Antony Gormley, will see 2,400 people occupy the plinth for an hour each, 24-hours a day, for 100 days.

Mr Parsons-Baker, from Moseley, was hoisted onto the plinth and drew laughter and applause from passers-by with his brown costume, made of foam with a leather covering, which has a large housefly attached to it. He held two placards saying “2.5bn people don’t have a toilet” and “G8 leaders – take action on the sanitation crisis now”.

Halfway through his hour he changed into a fish costume, putting a large foam fish on his back, to highlight the impact of over-fishing.

Deborah Symmonds, 47, from Oxford, who works in healthcare, said: “I thought ‘I’m in London today – I’m going to sit and observe for the morning and see the response of the people’.

“I come from South Africa originally. There are a lot of issues regarding water and sanitation there.

“I’ve always said that if I win the lottery, one of the first things I would do is try to make sure people have enough drinking water.”

Jessica Edwards, 36, a television producer from Camden, north London, said: “We are lucky we can come to a space like this, where people can voice their concerns and issues.

“More power to Antony Gormley, I say.”

Peter Hinton, 48, from Highbury, north London, who works for a company which invests in Africa said: “It’s a good cause. I’m not quite sure if it’s the right medium.”

Severn Trent Water worker Mr Parsons-Baker said after coming down: “I think it went brilliantly. I’ve had really good feedback. The crowd interaction was brilliant. I think they really got the message.

“I hope that people will donate to WaterAid, take an interest, and let’s hope for some action from the G8 on the sanitation crisis.”