Green Party MP Caroline Lucas complained to Twitter about a tweet from Brexit activist Arron Banks about Greta Thunberg, a climate change activist.
On Wednesday, Mr. Banks spoke about Ms. Thunberg's sea voyage across the Atlantic and tweeted: "Extreme recreational accidents occur in August …"
Thunberg, who chooses not to fly, leaves the UK for the UN climate summit in New York and Chile.
Ms. Lucas said to have reported on her comment, while Mr. Banks said it was a joke.
"Arron Banks' ugly tweet about @GretaThunberg is stinging my stomach," Lucas wrote Thursday morning on Twitter.
"I made a formal complaint on Twitter."
A spokeswoman for Twitter said, "We do not comment on individual accounts for privacy and security reasons.
"We take the threats of violence very seriously and act on the accounts if and when Twitter's rules are violated."
A source on Twitter told the BBC that the content did not violate its rules.
Thunberg departed Plymouth Wednesday at the start of her two-week trip to New York and Chile.
The 16-year-old pilot refuses to fly because of his environmental impact. So he chose a carbon neutral racing yacht.
Shortly after his departure, Banks, an insurance tycoon who founded Leave.EU, shared a tweet from Ms. Lucas who wished Mrs. Thunberg a "good trip".
His tweet has been the subject of much criticism. Mr. Banks then responded by saying that it was a "joke" and accusing his detractors of "not having a sense of humor".
Mr. Banks added later: "Of course, I do not hope she will meet a monster boating accident!"
"I only like to watch the ridiculous crowd tweet after the next bombing."
Among those who sentenced her post was actress Amanda Abbington, who tweeted: "You want a potentially fatal accident for a 16-year-old girl, why …?"
Others have called his tweet "shameful" while Labor MP Paula Sherriff said that he was "completely naughty".
The novelist Philip Pullman said, "It's like that you'll remember you, Banks – it's your measure."
According to Twitter, Anyone can post a tweet or individual profile for certain violations, including: spam, abusive or harmful content, inappropriate advertisements, self-harm and identity theft.
Fans rallied to signal to Mrs. Thunberg during her trip across the Atlantic.
Before leaving, she said about climate-skeptics: "There will always be people who do not understand or accept the United Science, and I will ignore them because I'm only acting and communicate about science. "
She added that she thought that mentalities were evolving "even if it is not enough and not fast enough, it is something, it is not for nothing".