Image copyright PA Media/BBC

Green Party MP Caroline Lucas has complained to Twitter over a tweet by Brexit campaigner Arron Banks aimed at climate change activist Greta Thunberg.

On Wednesday, Mr Banks referred to Ms Thunberg's sea voyage across the Atlantic and tweeted: "Freak yachting accidents do happen in August..."

Ms Thunberg, who chooses not to fly, is sailing from the UK to attend UN climate summits in New York and Chile.

Ms Lucas said she reported his comment, while Mr Banks said it was a joke.

"Arron Banks' vile tweet about @GretaThunberg makes me sick to the stomach," Ms Lucas wrote on Twitter on Thursday morning.

"I have made a formal complaint to Twitter."

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A spokeswoman from Twitter said: "We don't comment on individual accounts for privacy and security reasons.

"We take threats of violence very seriously and take action on accounts if and when the Twitter rules are violated."

A Twitter source told the BBC the content did not violate its rules.

Ms Thunberg set sail from Plymouth on Wednesday at the start of her two-week journey to New York and Chile.

The 16-year-old refuses to travel by air because of its environmental impact, so has chosen a carbon-neutral racing yacht.

Image caption Caroline Lucas - who used to be the Green Party leader - had wished Ms Thunberg a good trip

Shortly after she departed, Mr Banks, an insurance tycoon who founded Leave.EU, shared a tweet from Ms Lucas that wished Ms Thunberg "bon voyage".

His tweet faced widespread criticism, with Mr Banks later responding, saying it was "a joke" and accusing his critics of having "no sense of humour".

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Mr Banks later added: "Obviously I don't hope she encounters a freak yachting accident!

"I just enjoy watching the ludicrous tweeter mob following the next outrage."

Among those who condemned his post was actress Amanda Abbington, who tweeted: "You're wishing a potentially fatal accident onto a sixteen year old girl, why..?"

Others called his tweet "disgraceful" while Labour MP Paula Sherriff said he was "utterly vile".

The novelist Philip Pullman said: "That's how you'll be remembered, Banks. That's the measure of you."

According to Twitter, anybody can report an individual tweet or profile for certain violations, including: spam, abusive or harmful content, inappropriate ads, self-harm and impersonation.

Image copyright Getty Images Image caption Ms Thunberg set sail on the Malizia II, which was built for high-speed, long-distance endurance races around the world

Fans gathered to wave Ms Thunberg off on her voyage across the Atlantic.

Before leaving, she said of climate sceptics: "There's always going to be people who don't understand or accept the united science, and I will just ignore them, as I'm only acting and communicating on the science."

She added she thought people's mindsets were changing "even if it's not enough, and not fast enough, that's something, it's not for nothing".