A man stopped by police while swimming in the Thames early last Monday has admitted being foolish, but denies he was planning a protest.
Jonathan Hope, 32, told Sky News he is coming to the end of a year-long charity swim challenge, which involves him going for a swim every day of the year.
The challenge has seen him in waters across various parts of the UK but, as it comes to an end in November, he wanted to do something special to "round it off".
He decided that "it would be fun" to swim from near Downing Street towards Windsor, entering the water near New Scotland Yard in the early hours of Monday and setting off.
Mr Hope, who runs miso-making company Kultured, swam past the Palace of Westminster and was floating towards Lambeth Bridge when he was met by flashing blue lights and police officers.
His swim - which lasted roughly 20 minutes - was just days before the Queen was due to be lying in state at nearby Westminster Hall, and security in the area was even tighter than usual.
It was feared that Mr Hope could have been planning a protest, with an unnamed source telling the Mail Online that he was "likely a member of a green protest group...on a reconnaissance mission to gather information to disrupt preparations" for Monday's state funeral.
But Mr Hope was using a Go Pro camera attached to his head while he was swimming to post on his Instagram page as evidence of his charity challenge progress.
Mr Hope said: "This isn't a protest, I'm just trying to swim for charity.
"I need to do this before the water gets too cold (in the winter)."
He added: "The reason I was there at 2am was because the tide was high. It was very difficult to explain that to police - I guess it did look very suspicious.
"You can call me foolish or naive, but I didn't think there would be police there."
Mr Hope said he had been handcuffed and searched by police, but was not charged and let go with a warning.
Speaking about the incident involving Mr Hope, Commissioner Com Cundy said it had been "nothing more than a man that was going for a charity swim".
A force spokeswoman later confirmed that he was not arrested, but was "given words of advice about his proximity to a restricted area".
Mr Hope admitted that his partner was not impressed by his exploits, saying he has "a lot of grovelling to do".
"It's not how you want to start the week, really," he said. "I felt a bit foolish."
Thirty-four people arrested in lead-up to state funeral
Thirty-four other people, however, have been arrested in the lead-up to the Queen's funeral, according to the Metropolitan Police.
Deputy Assistant Commissioner Stuart Cundy said the arrests were for a range of offences, but none had been for protesting.
Mr Hope has raised more than £1,300 for his chosen charity Solidarity Sports, which helps traumatised children recover using the power of sport.