After receiving the call, an unidentified aide phoned Prowse back to reveal the Prime Minister’s favourite flowers were hydrangeas.
The comedian even gets away with a joke about Mr Trump grabbing Mrs May by the p***y instead of her hand.
Prowse claimed to be “Jeff Arnold”, an assistant to White House Press Secretary Sean Spicer in the Oval Office.
Heydon Prowse rang No10 claiming to be from the Oval Office
Ok, my hunch is hydrangeas
He was put through to Mrs May’s office and the aide replied she was not certain “off the top of her head” what the Prime Minister’s favourite flowers were but she would check and get back to him.
Moments later she calls back and asks: “Can I check who the gift is coming from?”
Prowse replies that “it’s essentially from Mr Trump” but that “Sean Spicer is organising it.”
The aide responds: “Ah yes, I see, excellent, fantastic. Ok, my hunch is hydrangeas."
- Trump 'warned his advisor may leave him open to BLACKMAIL from Russia'
- Government REJECTS Donald Trump state visit petition
The conversational turns even more comical when Prowse makes a deliberate slip up when he says he’ll send a card with a picture of Donald Trump grabbing Mrs May’s p***y instead of hand.
This is a reference to footage from 2005 when the Republican claimed as a celebrity he could “grab women by the p****”.
Prowse says: “I mean hand, sorry, I meant hand obviously, sorry that was a slip of the tongue.
Get Quotes on Home Insurance
“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?"
Trump Models: Donald's Legendary Supermodels Mon, January 30, 2017
Trump Model Management, founded by Donald Trump in 1999, is home to some of the most legendary models in the world.
1 of 28
The aide, who laughed at the slip up, then replies: “Of course I will certainly relay that message.” before the call ends.
The pranksters have since said they couldn’t believe the officials fell for the gag, even when they returned Prowse’s call on a UK mobile.
Prowse co-writes BBC political satire show Revolting, which includes a mock-reality spoof of Islamic State jihadists The Real Housewives of ISIS.
He said: "It's important not to pull your punches in satire. You have to be fearless or it undermines your credibility.”
Prowse writes and stars in the show alongside university friend Jolyon Rubinstein.
- Government drops plans for Donald Trump to address Parliament
- Actor says Hillary Clinton 'BEGGED him to leak racist Trump clip'
- Nigel Farage calls on Donald Trump to hold HUGE rally at Wembley