The Prime Minister’s LGBT adviser has said he is “dismayed” by the decision not to include transgender people in a ban on conversion therapy, while describing the cancellation of the Government’s landmark equality conference as an “act of self-harm by the LGBT lobby” .

Nick Herbert also called for a royal commission to “detoxify” and take the politics out of the trans debate.

It comes after the Government has faced fierce criticism over a series of U-turns last week on promised legislation to outlaw conversion therapy, and its backtracking on commitments to include transgender people in the ban.

At least 100 LGBT+ and HIV organizations pulled out of the UK’s first international conference on LGBT rights, Safe To Be Me, in protest, leading to its cancellation.

The anger has not been abated, with hundreds of people protesting against the Government’s decision outside Downing Street on Saturday.

Lord Herbert of South Downs, Boris Johnson’s special envoy on LGBT rights, wrote on his website: “The conference’s cancellation is damaging to the Government and to the UK’s global reputation.

“But it is also an act of self-harm by the LGBT lobby.”

He accused the LGBT+ charity Stonewall of orchestrating the boycott and of shedding “crocodile tears” over the subsequent cancellation.

Lord Herbert, 59, said: “LGBT groups were understandably dismayed, as was I, when a promised Conversion Therapy ban was suddenly dropped and then only partially reinstated just hours later”.

The exclusion of trans people reflected “concern that more time is needed to ensure that legitimate therapies to help young people with gender dysphoria are not inadvertently criminalized,” he said.

Such concerns can be allayed, he said, while warning ministers against conflating helping people with “ideology” that can “do irreparable harm”.

“We must address the concerns and make the case for change, deploying the evidence and reassuring parliamentarians that a ban which includes trans people is a safe and justifiable course to take,” he wrote, while criticizing “shouty protests” over the issue.

The former Conservative MP for Arundel and South Downs also said it was wrong to brand Mr Johnson as “transphobic” for saying last week that “biological males” should not compete in women’s sports and that women should have access to single-sex spaces in places such as hospitals and prisons.

Calling for a royal commission, Lord Herbert said: “We must not allow a descent into a political mire which is dominated by extremes and which suffocates the reasonable middle ground”.

Led by a senior judge and with “truly neutral” members, the inquiry would “examine these issues dispassionately”, he said.

“Weighing the evidence on contested areas such as sport, safe spaces for women, and gender identity services for children and young people… would be a better way to detoxify the debate, protect trans people from being caught in the political crossfire, and find the common ground we need.

“No-one will win from a culture war on these issues, and those most harmed will be trans people who already feel stigmatized, people who are different yet just like us, human beings who deserve greater kindness than today’s politics will allow”.

Meanwhile, hundreds of demonstrators gathered outside Downing Street to demand that transgender people be included in the proposed conversion therapy ban.

They shouted “keep trans in the ban” and “LGB with the T”, while many waved the pink, white and blue transgender pride flag.

Campaigner, Peter Tatchell, told the crowd: “We were promised a total ban.

“(Prime Minister Boris Johnson) has given us a half-baked ban, which we will never ever accept.

“The only ban worth having is a ban for everyone, including trans people.”

Jess, 23, from Nottingham, told the PA news agency that transgender people’s lives are at risk because of Government policy.

“The reason that I am here at the protest today is because Government policy and the transphobic rhetoric we’re seeing around excluding trans people from the conversion therapy ban is a massive threat to trans lives, particularly trans youth, within the UK,” they said.