Downing Street fooled by Valentine's Day prank

British Prime Minister's office fell prey to a Valentine's Day gag put up by a comedian claiming to offer flowers from US President Donald Trump to Theresa May, it emerged today.

An unidentified female No 10 Downing Street aide revealed hydrangeas - a type of plant native to southern and eastern Asia and the Americas - were May's favourite flowers after ringing serial trickster Heydon Prowse back on his mobile number.

During the six-minute exchange, the prankster claimed to be "Jeff Arnold", an assistant to White House Press Secretary Sean Spicer in the Oval Office, 'The Sun' reported.

After being put through to the British prime minister's office, he asked what May's favourite flowers were because they "want to send something really nice for Valentine's Day".

The aide said she's not 100 per cent sure "off the top of her head" but said she will check and get back to him.

She ringed him back a short while later asking: "Can I check who the gift is coming from?" The prankster replied: "It's essentially from Mr Trump but Sean Spicer is organising it."

She then responded: "Ah yes, I see, excellent, fantastic. Ok, my hunch is hydrangeas."

The prankster exclaimed: "Hydrangeas, absolutely fabulous, ok", before the aide interrupted to reveal May is a "keen gardener".

"We'll send over a lovely Valentine's gift. Please pass Mr Trump's regards onto Theresa because really he is such a lovely man and he had such a lovely time with Theresa he just wants to pass than onto her, ok?"

The aide then replied: "Of course I will certainly relay that message," before the call ended.

The pranksters said they couldn't believe May's officials didn't realise even when they left a local UK mobile to call back on.

Joe Wade, from the Don't Panic advertising agency behind the sting, said they were shocked aides fell for the joke.

Agency founder Joe Wade told the newspaper: "We thought this was a fun thing to do to celebrate Valentine's Day. "It was a spontaneous idea to show how special Donald Trump and Theresa May's relationship is.

"Donald Trump is a comical character. We just want to make people think about things in a slightly different way."

Comedian Heydon Prowse previously managed to get past staff and security at former British Prime Minister Tony Blair's home in central London – pretending to measure up for a commemorative stained glass window.