Activists inflate a giant balloon depicting US President Donald Trump as an orange baby in north London on July 10, 2018.
President Trump will head to London on Friday, where he's expected to face protests at every turn.
Gardner, who works with refugees as part of her doctoral research at the London School of Economics, said Trump's speeches about refugees and immigrants are "a very risky line of rhetoric to be normalized".
On Friday, Trump will meet May and her newly appointed Foreign Secretary Jeremy Hunt at the prime minister's countryside retreat, Chequers.
U.S. Ambassador Woody Johnson said Wednesday that citizens are often advised to avoid public demonstrations and that he is not upset by the decision to allow the "Trump baby" balloon to be displayed near Parliament.
Like this go-round, protesters promised widespread backlash back in February amid the president's plans to travel to London for the grand-opening of a new USA embassy.
As well as meeting the Queen at Windsor, also on Mr Trump's schedule is a journey to Scotland where he owns two golf courses and will spend the weekend.
Assistant Chief Constable Mark Williams said: "Clearly there is a significant protection operation in place for the president and this includes restrictions to the airspace in the Turnberry area".
US President Donald Trump arrives in Britain on Thursday for talks with the leader of the United States' closest ally in Europe.
"The UK loves me, in fact my mother was from the UK, they love me there even if they are not treating us well with trades, but they will", he said.
May will seek to put the tensions behind her when she hosts Trump later Thursday for a black-tie dinner with business leaders at Blenheim Palace, the birthplace of World War II prime minister Winston Churchill.
Protesters are set to descend on the Regent's Park residence, with plans to blare out recordings of children crying for their parents at USA detention centres.
Protests are expected against Trump, whose policies - including a travel ban on a number of predominantly Muslim countries, detention of child migrants on the US-Mexico border and imposition of tariffs on European Union steel and aluminium exports - have all been criticised by the UK.