By Mark White, home affairs correspondent
The Labour leader Jeremy Corbyn will join thousands of anti-Trump protesters on the streets of central London today, as Scotland Yard's Commissioner warns her officers will take firm action against any protesters who break the law.
Mr Corbyn, who snubbed last night's state dinner at Buckingham Palace, said he wanted to show solidarity with demonstrators and planned to address the protest.
A huge police and security operation is in place for the US President's three-day trip and severe restrictions have been placed on areas where Mr Trump will visit, preventing the public from getting too close.
Last year, almost 10,000 officers were deployed for Mr Trump's trip to the UK, with nearly every force in the country providing staff to support the operation.
This year's state visit is even bigger, as the Metropolitan Police said it had "a very experienced command team" leading the operation.
Wherever the US President goes, there is always a well-rehearsed security plan and US secret service agents have been mingling with their British policing colleagues and members of the public.
But Sky's policing analyst Graham Wettone said the addition of large numbers of protesters makes events much more unpredictable.
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"The difficulty is, you've got a huge a security operation, but you don't really know what the protesters and demonstrators are going to do. If they decide to do something that isn't either known about or authorities are aware of, that makes it really complex for the police to respond and react to that," he said.
Protesters are again hoping to fly the Donald Trump blimp, which depicts the American leader as a giant yellow baby.
A 16ft talking robot of Mr Trump sitting on a gold toilet is also expected to make an appearance.
Supporters of Human Rights charity Amnesty will also unfurl five giant banners from Vauxhall Bridge, facing the US embassy, saying "Resist sexism", "Resist racism", "Resist hate", "Resist cruelty" and "Resist Trump".
In Finsbury Park, north London, organisers of today's No To Trump rally said that many people had expressed interest in attending.
Organiser Terina Hine said: "He has torn up the Iran nuclear deal, an international trade treaty, he's threatened war with Iran, he's a threat to world peace, the list is endless.
"The government is currently rolling out the red carpet to Donald Trump and we think that as a racist, misogynist, warmonger, that this should not be the case.
"I think the vast majority of people in the UK don't support Donald Trump's politics. We had thousands of people out there on the streets of London the last time he visited, so hopefully there will be even more on the streets this time round."
Not everyone on the streets of central London is opposed to the Trump visit.
Ed Epstein, a tourist from Seattle, joined several thousand outside Buckingham as the President arrivedRead More – Source