Heather Mills has launched a new campaign urging people to adopt a more plant-based diet by asking: "Why don't we drink rats' milk?"

The campaign for animal rights organisation Viva claims that dairy and meat products are a major cause of greenhouse gases.

Mills said: "When (Viva) told me it was 18 per cent, that's more than all global transport, I was in shock. Aeroplanes only bring 3 per cent, while they are being picked on with taxes."

She called on people to "cut down on one or two meat and dairy and fish dishes a week", adding: "I'm not saying people need to go vegan overnight."

Mills said: "We are the only species that drinks another person's milk, so why aren't we drinking rat's milk, or dog's milk, or cat's milk, that's how crazy it is?

"It's mad that we are having cow's milk. Even cows don't drink it after one year but we continue forever."

The 39-year-old posed in front of a giant mobile billboard bearing her image.

The poster featured her in sultry pose and low-cut sequinned vest beside the slogan: "Hey Meaty, you're making me so hot!"

The publicity launch at Speakers' Corner in London's Hyde Park began with what some interpreted as a dig at her estranged husband, Sir Paul McCartney.

When the billboard arrived it bore a giant poster for a domestic violence hotline, which was then removed to reveal the Viva ads.

Leaked legal documents alleged that former Beatle Sir Paul had been violent towards his wife.

However, a spokeswoman for Mills said the presence of the domestic violence poster was pure coincidence.

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