Ministers are braced for a potential flying visit by Donald Trump to Britain in the coming weeks, it is understood.
Officials believe the US president may have a window in his schedule to drop in on one of his golf courses in Scotland, which are in Aberdeenshire and Turnberry, Ayrshire, as he has several visits planned in Europe in July.
Mr Trump is in Poland on Thursday before attending the G20 leaders' summit in Hamburg in Germany on Friday and Saturday.
He will also attend the Bastille Day celebrations in France on July 14 and the Government is on alert for a potential visit to the UK.
The news prompted campaigners to urge opponents of the controversial tycoon to be "on standby" for street demonstrations, describing him as a "racist" and "misogynist".
According to the Sunday Times, Mr Trump will only confirm his plans to the Government 24 hours in advance, and he may also drop in on Downing Street.
Once confirmed, it is believed that officials and ministers would then have to make arrangements for a visit, including a potential meeting with Theresa May or other senior ministers.
Owen Jones, co-founder of Stop Trump Coalition, said: "Donald Trump is so cowardly he thinks he can sneak into the country to avoid protests.
"We have to prove him wrong. We're asking Britain to be on standby to take to the streets with just hours notice if necessary.
"Let's not allow the arrival of a misogynist, a racist, a bigot, and a threat to peace be unchallenged. Let's take to the street in great number - and do ourselves proud by showing that Britain rejects his hatred."
The charity War On Want said: "Millions of British citizens have already sent a very clear message to the Government that the racism, bigotry and hatred of Donald Trump is not welcome here.
"Any attempt to sneak him into the country and offer Trump a veneer of respectability for his divisive and reactionary policies will be utterly rejected."
Shaista Aziz, founder of The Everyday Bigotry Project, said: "Trump's dangerously divisive presidency and casual everyday bigotry mirrors a huge spike in racist and homophobic hate crime in the USA and the further criminalisation and demonisation of Muslims, immigrants and refugees.
"He is not fit to hold the office of the US presidency and he's absolutely not welcome in the UK - through the back door or on an official state visit."
The Government has insisted a separate and contentious state visit to Britain will go ahead despite it not being listed in the Queen's Speech.
The address to Parliament usually mentions planned state visits but last month's edition only contained a reference to welcoming King Felipe and Queen Letizia of Spain in July, despite the Prime Minister extending an invitation to the US president just a week after his inauguration.
Speculation that the visit had been put on the backburner came after the White House denied reports that Mr Trump told Mrs May he does not want to go ahead with the trip if it is going to lead to large-scale demonstrations.