Annie Lennox and Miriam Margolyes are among artists who have accused the Metropolitan police of giving preferential treatment to a far-right demonstration led by Tommy Robinson over a pro-Palestine protest in London on the same day.

The pro-Palestine movement has had its preferred route through central London for its annual commemoration of Nakba – the mass expulsion of Palestinians – rejected by the Met, while the “Unite the Kingdom” demonstration will take place on the same date in Kingsway, the Strand, Trafalgar Square, Whitehall and Parliament Square. Robinson, whose real name is Stephen Yaxley-Lennon, posted on X: “London is ours on May 16th.”

An open letter saying that the Met “must not favour the far right over Palestine” has also been signed by the actors Samuel West and Khalid Abdalla, the musicians Billy Bragg and Nadine Shah, as well as MPs, academics, lawyers, trade union and civil society leaders. The Met said the decision was based on the relative scale of the demonstrations.

Billy Howle, who starred in the TV shows The Perfect Couple and The Serpent and also signed the letter, said: “The shocking decision of the police to exclusively favour a far-right demonstration and block this important annual commemoration from the political heart of London will send shivers down the spines of every person of good conscience. It must be overturned.”

The letter says that the pro-Palestine movement informed the force on 18 December of its intention to march on the nearest Saturday to Nakba Day, in keeping with a tradition dating back more than a decade, but that the Met has “instead given over the political centre of London to a hate march called by racist thug ‘Tommy Robinson’”. It calls on the force to “immediately reverse this shameful decision”.

The route for the Nakba march has still not been finalised, with organisers concerned about the risks to participants posed by the far right, which the letter says has previously carried out “verbal and physical violence directed at the movement and the police”.

The Met’s decisions on the two marches come amid claims of increasing repression of Palestinian solidarity marches. Routes and timings have previously been restricted and in December the Met and Greater Manchester police said they would arrest anyone chanting the words “globalise the intifada” or holding a placard with the phrase on it, citing fear in Jewish communities. Intifada means uprising or resistance and pro-Palestinian figures have denied it is a call for violence.

On Thursday, more than 30 MPs, led by Labour’s Andy McDonald and Kim Johnson, who have also signed the letter to the Met, tabled a motion to reject the government’s proposal to require police to consider the “cumulative impact” of repeated protests in the same area – drawn up in response to pro-Palestine demonstrations – when imposing conditions.

A Met spokesperson said decisions on demonstrations were not based on political affiliations but on safety and security. They said it could be “reasonably anticipated given the number of attendees at the last event organised by the same group” that the far-right event would attract “very significant crowds”, adding: “There are only a limited number of roads in central London that can be used to safely accommodate such a crowd, with Whitehall being the most suitable.”

They said the force would be open to meeting the organisers of the Nakba Day protest to agree an alternative location.

Separately, the Met said on Friday it was expecting “criminal offences” at Saturday’s Defend Our Juries demonstration in Trafalgar Square, central London, opposing the proscription of Palestine Action.

The ban was ruled unlawful by the high court in February, leading the Met to say it would stop arresting people for alleged support of the direct action group. But last month it said it would resume arrests given the ban remained in place pending the government’s appeal against the court’s decision.