Players in England's top flight have been going down on one knee before kick-off since George Floyd, who was black, was killed by a white police officer in the United States last year
England is preparing to host its biggest football party for a generation but home matches at Euro 2020 risk being overshadowed by a row over players taking the knee to highlight racial injustice.
Manager Gareth Southgate says his England players will continue the kneeling gesture adopted in the Premier League, despite boos by some fans before recent friendlies against Austria and Romania.
The jeers were drowned out by applause at Middlesbrough's Riverside Stadium, but there are fears England's European Championship opener against Croatia on Sunday could be blighted by an embarrassing repeat.
Players in England's top flight have been going down on one knee before kick-off since George Floyd, who was black, was killed by a white police officer in the United States last year.
Matches had largely taken place in empty stadiums as a result of coronavirus restrictions, but now fans are back the issue has been thrust front and centre.
All three of England's group matches are at Wembley, as are the semi-finals and final of the pan-European tournament, turning it into a virtual home event for Southgate's men.
They will also play at Wembley in the last 16 should they top Group D.
Brendan Clarke-Smith, a lawmaker for Britain's ruling Conservative Party, wrote on Facebook that taking the knee "now comes across as little more than habitual tokenism and has lost its effect".
In contrast, the opposition Labour party's John McDonnell said the booing of the gesture was "racism".
Prime Minister Boris Johnson was initially equivocal over the booing but his spokesman has made it clear that he "would like everyone to get behind the team to cheer them on, not boo".
Ex-NFL quarterback Colin Kaepernick started kneeling to protest against racial injustice in 2016 and the gesture has become a familiar sight across a range of sports since the Floyd murder.
Piara Powar, executive director of anti-discrimination organisation the Fare Network, told AFP that taking the knee was still a meaningful act, which had sparked a "culture war-type debate".
"It is something that is impactful," he said. "If it wasn't impactful, people wouldn't be booing it."
Fare is sending observers to Euro 2020 matches that are deemed high-risk for incidents of discrimination and will give feedback to European governing body UEFA.
Powar said critics linking the taking of the knee narrowly to the politics of the Black Lives Matter organisation missed the point that it dates back to the US civil rights protests of the 1960s -- Martin Luther King adopted a similar pose -- and has become a symbol of a sporting movement against injustice.
"I think those that are trying to decry it by linking it to the British BLM organisation are incorrect and I think they know that," he said.
"What's happening now is you have many Conservative MPs, you have the prime minister, who just don't like the fact that it's taking place and that's the sad fact."
Powar pointed out the relatively small number of fans booing at the Riverside Stadium and said he expected a different story at Wembley for the Euro 2020 matches.
But others believe taking the knee has lost its power.
Crystal Palace forward Wilfried Zaha earlier this year stopped the gesture, saying it was "degrading", while a number of clubs in the second-tier Championship made the same decision.
One England fan told the BBC he booed in Middlesbrough to show his objection to an "identity politics agenda" being brought into football that focuses on skin colour.
"Booing is a way football fans can communicate dissatisfaction," he said. "Some seem to genuinely believe booing is an act of racism -- I reject that."
A UEFA spokesman stressed the organisation's "zero tolerance" attitude towards racism on the eve of the tournament.
"Any player who wants to demand equality amongst human beings by taking the knee will be allowed to do so," he said.
"We urge spectators to show respect for teams and players taking the knee."