Impressionist Alistair McGowan joined campaigners as they hung clothes on thousands of metres of line to highlight the fact that if every family hung out their washing rather than using a tumble direr just once a week the UK would save £88 million on its annual electricity bills, and 550,000 tonnes of carbon emissions.

The stunt was described by its creator the bearded comedian and eco-warrior Tim Higham as the biggest one-line joke in history.

He already holds world records for rowing the Channel in a bath and the longest distance travelled in a boat made of paper (recycled, naturally).

But behind the fun was a serious message that if we all did a few little things to help the environment we could have a huge collective impact.

The Environment Agency had also set out its stall in the famous square, calling on people to make up to ten pledges to protect the environment – among them, to stop using tumble driers, alongside the more familiar requests to turn off taps when brushing our teeth, find more sustainable ways to commute to work and not over-fill kettles.

“There are events taking place today all over the world to draw attention to the environment, the damage we’re doing to it and what can be done about that,” said McGowan.

“I feel passionately about the world and the amount of waste we are producing – we’ve taken our eye off the ball.

“All this stuff [the EA’s promises ask us to do] seems so simple, yet we’re not doing it.

“We need to get the message out there and show what could be done – today is the day we draw attention to it, but this is a commitment we need to make for the rest of our lives.”

Sir John Harman, chairman of the Environment Agency, said: “World Environment Day is a really important thing. People often say to me, global climate change is a really major thing, but what can I do? What difference can I make?

“The message we’re trying to get across is that you can do a lot of very simple things and provided enough of us do them it will make a big difference.

“I hope everybody signs up to one or more of these ten pledges.”

This is the third year the agency has called on the public to pledge their support for the environment and real progress has been made through the campaign.

“It’s all about raising awareness,” The EA’s Jo Fox told edie.

“We’ve seen a lot of progress of the past ten years since the Environment Agency was set up – rivers are cleaner, there are more fish and biodiversity is recovering.

“But there is still a lot to do and when faced by such a big thing people often wonder what they can do themselves.

“Sometimes as one person you think you can’t make much of a difference.

“But if we all do a few of these simple things the collective difference will be huge.”

Sam Bond

Action inspires action. Stay ahead of the curve with sustainability and energy newsletters from edie