London - (Reuterus): The news comes amid an official announcement that President Obama and his wife Michelle are coming to the UK on a state visit in May.
"At this stage we simply don't know what is Palace protocol about shagging the current US incumbent," diplomatic sources admitted tonight.
Queen Elizabeth's presidential humping track record goes back to a 1953 two minute knee trembler behind Palace stables with Ike Eisenhower.
Despite premonitions that she was a 'black widow' kind of monarch who'd kill him soon after the act of copulation a heavily sedated Jack Kennedy was next.
Lyndon B Johnson ought have taken his place in the line-up but was warned off by the CIA 'that she'd bump him off just like JFK' for failing to fully satisfy her.
Richard Nixon came off lightly with an oral quickie in a Windsor Castle potting shed, while his successor Gerald Ford needed hypnotherapy before and after the dirty deed.
Then along came her brother Ronald Reagan who'd been an having incestuous relationship with his sister Elizabeth II ever since the two were out of diapers circa 1935.
Even so his 1983 state visit to Windsor Castle saw him needing two years of colonic irrigation to rid the digestive tract of 'something he'd swallowed' during his last fateful romp with her.
President George H Bush's attentions had originally come nearly 40 years earlier when he fathered their love child Peter Sutcliffe, aka the Yorkshire Ripper.
He lost no time in rekindling the relationship despite deaths threats from Prince Philip who complained about catching some kind of STD a few days after Bush Senior's last state visit.
Forty second US President William Jefferson Clinton needed no prompting about what was expected of him in the royal sack - despite being HM's very own son by the Queen Mother's bastard spawn Sir Terence Con Artist.
When George W Bush dropped by in the autumn of 2003, laden down with viagra and electronic sex toys, the Queen claimed to be 'indisposed' with a headache.
In the end Bush Jr got a brief handjob from HM which Laura videoed for the family archives.
How Barry Obama will come off in May is anybody's guess.
"He might cry off in the end, say he's got a period - or whatever," an embassy spokesman admitted ruefully.