An employment lawyer who questioned the Conservative leadership candidates during the BBC’s televised debate has become the second member of the public featured on the programme to be suspended from their job over controversial social media comments.

Solicitor Aman Thakar, the Labour candidate in Borough and Bankside in the Southwark local election last year, has been suspended with immediate effect by Leigh Day while the law firm investigates one of his previous tweets.

Screenshots taken before Mr Thakar made his Twitter account private showed he once tweeted: “Hitler’s abuse of the term nationalism is, to me a nationalist, the most harmful part of his legacy”.

On Wednesday evening he tweeted: “Context on my tweets regarding Hitler, my full and sincere apologies for any offence caused”.

He said he had commented on a speech by US conservative commentator Candace Owens which had discussed Hitler and nationalism. “Was me being sarcastic about this speech, Candace Owens was defending nationalism, hence I said “to me a nationalist”, and said sarcastically as a nationalist the abuse of the term was the worst part of his legacy.

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“This is not my point of view, I was being sarcastic about the speech that was given and hope this provides you with the full context of the comment,” he added.

It is the latest fallout from the BBC debate, after imam Abdullah Patel – one of the others chosen to ask the Tory candidates a question – was suspended from his mosque and the Gloucester school where he works as deputy headteacher after criticism for allegedly antisemitic tweets about Israel.

The BBC has been forced to defend its vetting process following the job suspensions. “Last night’s questioners held a range of political views and we did not specify these views nor their backgrounds although some chose to do so themselves,” said a spokesman.

The spokesman added: “The last questioner on the debate is a solicitor who was seconded by his law firm to the Labour Party in the past, rather than being a Labour “staffer”. He is a Labour supporter and once stood as a councillor.”

Mr Thakar, the London solicitor who did not declare his previous Labour affiliation on screen, asked the candidates when they would call a general election after saying they would have “no mandate from the people”.

Leigh Day said it was taking his tweet “very seriously”.

Mr Patel, who asked the contenders about Islamophobia during a BBC debate on Tuesday evening, was criticised for past tweets in which he said “every political figure on the Zionist’s payroll is scaring the world about Corbyn”.

He also shared an image endorsing the relocation of Israel to the US as a way of solving the Israel-Palestine conflict.

The BBC said Mr Patel would not have been picked if it had been aware of his previous comments, and said his Twitter account had been deactivated ahead of his appearance, meaning the old tweets could not be read. “Had we been aware of the views he expressed he would not have been selected,” the broadcaster said.

Imam Abdullah Patel warns our future prime minister panel that Islamophobic 'words have consequences'

The executive members of the Masjid e Umar mosque in Gloucester said of the imam’s suspension: “We have decided to act immediately and have chosen to give him some time away to allow us the opportunity to conduct a detailed investigation into this matter.

“This is the official stance of the mosque’s executive committee and we hope you respect our right to privacy as we conduct this deeply sensitive investigation.”

Al-Ashraf Primary School in Gloucester said in a statement posted on its website that it had suspended Mr Patel, who is the deputy headteacher, from all school duties.

Yakub Patel, chairman of Al-Madani Educational Trust, said: “Following some of the comments attributed to Mr Patel in the media this morning, the Trust has decided to suspend him from all school duties with immediate effect until a full investigation is carried out. The school and Trust do not share the views attributed to him.”

Tory leadership candidates criticised the broadcaster’s handling of the public questions on the TV debate, and members of their camps have suggested it could impact on whether they agree to another televised hustings on the BBC before the contest ends.

“It will play into our thinking as to whether we agree or don’t agree to another BBC event,” an aide of Sajid Javid told The Telegraph. A source close to Jeremy Hunt added: “We are reserving judgement but it’s fair to say we didn't think it was brilliant.”

Earlier on Wednesday the home secretary urged Mr Patel to “practise what he preaches” and said that words “do indeed have consequences”.

The Tory candidate tweeted: “All of us in public life have a duty to be vigilant for antisemitism & anti-Muslim prejudice. I never imagined we would see it rising in 21st century UK. Unlike the Labour leadership, which is itself part of the problem, my party takes that duty seriously.”

BBC Radio 5 Live presenter Nicky Campbell, who had Mr Patel on his breakfast show, tweeted: “I would like to apologise. We had the imam from the BBC Tory leadership debate on our programme this morning. His social media comments have been extremely disturbing. We should have checked. We didn’t. I’m sorry.”