The shadow foreign secretary, Emily Thornberry, has said a Labour government would engage in a businesslike way with Donald Trump but would not afford special honours to the US president.

Speaking before a mass demonstration in London on Tuesday, which will be addressed by the Labour leader, Jeremy Corbyn, Thornberry said: “A state visit is an honour and we don’t think this president deserves an honour.

“The truth is he has tried to close borders with Muslim-majority countries, he is caging small Mexican children, he has grabbed women and boasted about it. He is a sexual predator, he is a racist and it’s right to say that – we need to think about when is it our country got so scared?” she told BBC Radio 4’s Today programme.

Thornberry said Corbyn’s attendance at a state banquet for the Chinese president, Xi Jinping, was a different situation.

“When you have a close friend and they’re going wrong, you are more likely to be adamant with them and clearer with them than someone who has not been as close a friend and someone you are trying to build a relationship up with,” she said.

Thornberry, speaking earlier on ITV’s Good Morning Britain, said Labour would not refuse to engage with Trump, but would do so without pomp and ceremony.

“When I become foreign secretary, I hope that what he will respect and understand is a certain amount of strength and an ability to be able to say what it is that you think, and not be bullied and kowtowed and shouted over. And say Britain is a friend of a America, you are going wrong,” she said.

The shadow foreign secretary called the government’s attitude “pusillanimous, it’s too weak, it doesn’t stand up to him”, and said the president “undermines the world order” in a hugely risky way.

“We’ll talk to him but not in front of the Queen. We’d have a business meeting,” she said.

Thornberry said she had written to Buckingham Palace to pre-emptively decline an invitation to the state dinner hosted by the Queen at the palace on Monday night, which Corbyn also declined to attend.

“I didn’t want to embarrass the palace by them sending an invitation and me saying no. So I wrote and pre-empted it,” she said.

“The Queen invited the president over on the advice of the prime minister. That advice was wrong. I’m not saying that he should not come and have business meetings, I’m not saying we shouldn’t talk to him, but the things I want to say to President Trump I probably shouldn’t say in front of Her Majesty. We would end up having an argument.”

A huge police and security operation was under way on Tuesday morning, with protesters barred from demonstrating directly outside Downing Street and road closures in place.

Organisers of the Together Against Trump protest have billed the day as a “carnival of resistance”, with demonstrators gathering at Trafalgar Square from 11am to declare a “Trump-free zone”.

Demonstrators will not be permitted to march past Downing Street, as part of Whitehall will be closed off, the Metropolitan police confirmed on Monday afternoon. Organisers had initially planned to demonstrate outside the entrance to Downing Street as Trump held talks at No 10.

Theresa May, who is hosting the US president as one of the final acts of her premiership, will not hold a one-on-one bilateral meeting with him, but will host Trump in Downing Street on Tuesday for a series of events, including a press conference later in the afternoon.

She will insist the relationship between the US and the UK is “a great partnership, but one I believe we can make greater still”.

The two leaders will jointly host a business breakfast with US and UK companies, highlighting the claimed benefits of a post-Brexit bilateral free-trade deal. Trump has tweeted that a “big trade deal is possible once UK gets rid of the shackles [of the EU]”.

About 250,000 anti-Trump activists gathered when he flew into the UK in July last year for his first visit as US president.

Protests are also planned in Birmingham, Stoke, Sheffield, Glasgow, Edinburgh, Chester, Leicester, Oxford and Exeter.