Emily Thornberry has dismissed attacks on her new role as shadow defence secretary, after she was linked to a controversial legal firm accused of “hounding” British soldiers.

The Islington South and Finsbury MP was only promoted to the shadow cabinet role last Wednesday. But she has come under attack by Conservative MPs and national media after it was revealed she received donations from Clerkenwell-based Leigh Day.

Last Tuesday, Leigh Day was referred to the Solicitors Disciplinary Tribunal over its role handling legal challenges of hundreds of Iraqis during the Al-Sweady inquiry. They claimed they were abused and unlawfully detained by British forces in 2004, but this was rejected by the inquiry.

Leigh Day, representing the Iraqis, was accused of “falsity” by Michael Fallon, secretary of state for defence. Conservative MP Stewart Jackson spoke against Mrs Thornberry in Parliament last week, and also labelled the St John’s Square firm “immoral”, accusing it of “hounding” British soldiers. Leigh Day has denied all allegations.

But Mrs Thornberry told the Gazette this morning she has nothing to hide, as Leigh Day’s donations - sending legal research assistants to work in her office - came before the inquiry ended in December 2014.

And a parliamentary register of financial interests, released on Monday, shows that Mrs Thornberry accepted an assistant between September 2013 and March 2014, and another between September 2014 and November 20 of that year. This was the day she was forced to resign from her position as shadow attorney general after being accused of snobbery.

She said: “When I asked for help in my office, I didn’t have any resources and shadow attorney general was a big job. I managed to get officers on secondment after I persuaded Leigh Day. It was really helpful as these were some of the brightest young people in the profession.

“I think that’s fair enough because this (referral to the tribunal) hadn’t happened. This story is an attack by the Conservative Party central office. It doesn’t have any substance.”

She added: “If you start criticising lawyers for taking on certain cases, the role of law stops. It’s their duty to be a mouthpiece; an advocate. It’s for the tribunal to decide where this case goes.”

The second Leigh Day donation, between September 2014 and November 2014, was only registered by Mrs Thornberry on Monday. Asked why, she admitted she forgot amid the fallout of her resignation.

“This was pointed out to me by the Daily Telegraph, at which point I registered the donation. I forgot. I had lost my job and quite frankly, I was upset. It was an unfortunate combination and not even the Tories can lay the blame on that.”

A statement on Leigh Day’s website denied all allegations and said: “Leigh Day believes the decision to refer the firm to the Solicitors Disciplinary Tribunal is premature as it has not been given a proper opportunity to respond.”