The mother of an environmentalist who threw green slime over Business Secretary Lord Mandelson has spoken of how proud she is of her daughter.

Leila Deen, 29, from campaign group Plane Stupid, became famous yesterday when she threw a cup of green custard into the minister's face as he arrived for the Government's low carbon economy summit in central London.

Leila Deen coats Peter Mandelson

At the family home in Valley Drive, Brighton, mother Sheila Deen, 60, told The Argus: "I'm proud of her. She's got the courage to take action to address what she says is an injustice.

"She has campaigned for several years now on issues such as Kingsnorth coal-fired power station, Heathrow's third runway and others that have a disastrous effect on people in developing countries.

"What she is saying is that we must take responsibility for the damage we are causing to our planet.

"She's always had the determination to pursue these issues and to try and make an impact.

"Whereas I feel quite strongly about them I don't think I would do the direct action she does but that's not to say I disagree with it."

Mrs Deen, a teacher at Westdene Primary School, Brighton, said her daughter had been aware of green issues since a child as she herself was a member of Greenpeace.

After doing a degree in international development at the University of Leeds, Leila went on to do a master's degree at the University of Sussex.

Mrs Deen said she believed Leila had not flown for about three years and had been involved in Plane Stupid for a similar period.

Over the New Year Mrs Deen celebrated her 60th birthday by going on a trip to Morocco by train with Leila and her sister, Emma, 31.

Ms Deen, who works for the World Development Movement, said her protest was against Lord Mandelson after it was suggested he met lobbyists from Heathrow owner BAA before the Government gave the final go-ahead for a third runway there.

She said: "The only thing green about Peter Mandelson is the slime coursing through his veins. That Mandelson is trying to make political capital out of climate change just days after reports that he met BAA's top lobbyists to push through the third runway is an insult."

The Metropolitan Police has launched an investigation into the incident.