Anti-Heathrow expansion activists were out and about at the weekend keeping up the pressure on the government to think again about plans for a third runway at Heathrow Airport. This time they took to the streets - literally - to get the message across, using a new method called 'clean grafitti'.
Taking a cue from the "wash me" messages scrawled on the back of delivery trucks, clean (or reverse) graffiti uses high-pressure steam to imprint images on dirty walls and pavements.