Two men and a woman have been arrested after Greenpeace activists in kayaks and boats boarded a 23,498-tonne ship on a major import route bringing Volkswagen diesel cars into the UK.

The clean air campaigners drew up alongside the huge car carrier in the Thames Estuary around 8.30am this morning.

They hung from the 27-metre-high unloading door and said they would not disembark until VW commited to take its "toxic cars" back to Germany.

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Meanwhile, more than 40 volunteers scaled the fences at Sheerness docks – the intended destination of the ship – and gained access to the vehicle park, where several thousand VW cars are awaiting distribution to suppliers.

The volunteers attempted to immobilise all of the VW diesel cars by removing the keys.

They also lifted the bonnets and labelled the engines with messages from 8,000 people, including many car owners, calling on VW to ditch diesel.

The German car giant imports tens of thousands of vehicles through Sheerness, one of Britain’s largest car ports, every year.

Video: Greenpeace during this morning's action

Janet Barker, a support worker from Powys, Wales, and one of the volunteers taking action, said: "Diesel cars are toxic – so we’re here to block VW imports on behalf of all of the children who are the most acutely affected by the health impacts of diesel fumes.

"VW’s polluting vehicles are adding to a public health emergency harming thousands of people."

She added: "The government says we need to wait another 23 years for dirty diesels to be banned. We can’t wait that long. So we’re stepping in and seizing all of VW’s diesel cars to stop them harming people’s health and the environment.

"We’re not leaving until VW takes its toxic cars back to Germany. As Europe’s largest car maker, VW needs to wake up, smell the emissions and go fully electric.”

Campaigners say it was two years ago VW was caught "cheating" on emissions tests, but "despite its attempts to look like it’s moving to electric, it still has no plans to ditch diesel".

Activists have hung a 50 square metre banner on the ship's unloading ramp showing the face of two-year-old Sephie covered by an air pollution mask.

She has respiratory problems and represents all children affected by air pollution.

Pennant banners emblazoned with Sephie’s portrait were also hoisted on gantries surrounding the vast car park.

A Peel Ports spokesman said Greenpeace protesters had "illegally entered secure areas" of the Port of Sheerness.

He added: "These areas are restricted to ensure that UK border security is preserved and we protect the safety of our customers and employees working on the Port.

"We are working with the police, Greenpeace and Volkswagen to resolve the situation.

"The safety of the protesters and employees, whilst safeguarding the marine environment, remains our principal priority.”

Police were called to the port shortly before 9am.

A spokesman said officers' primary role was to "facilitate a peaceful protest, to prevent and detect crime and disorder and to ensure the safety of the public, the protestors and the police".

He confirmed one man had been detained on suspicion of aggravated trespass, while the other man and a woman were arrested under the Merchant Shipping Act 1995 on suspicion of entering a vessel.