An MP supporting an SAS sniper jailed for illegally possessing a gun said visiting the father-of-two had "filled him with determination" to get justice for him.
Julian Brazier, MP for Canterbury and Whitstable, visited Sergeant Danny Nightingale at the Military Corrective Training Centre in Colchester, Essex on Monday.
Sally Nightingale says her husband is "struggling with being locked up for 16 hours a day"
Sgt Nightingale, who served in Iraq and Afghanistan, was sentenced to 18 months in military detention by a court martial after pleading guilty to possession of a prohibited firearm and ammunition.
The controversial case has sparked outrage from SAS veterans and Mr Brazier, a former captain in the SAS reserves, has secured a short debate on the case for Tuesday evening.
After visiting Sgt Nightingale on Monday evening he said: "It was humbling in a way to feel that such a guy, who has given so many years service could have been brought so low by a system of which I am part, the legislature.
"It filled me with a determination that we have to get justice for this guy."
Sgt Nightingale's wife, Sally, visited him on Sunday for the first time since he was sentenced two weeks ago.
Mrs Nightingale, who has written to prime minister David Cameron urging him to intervene, said her husband was "struggling with being locked up for 16 hours a day".
"He was trained to deal with being detained by the enemy - it is impossible for him to understand how he has found himself detained at the hands of the country he has served so loyally for over 17 years," she said.
She said her husband was finding his situation difficult but was "humbled" by the public's support.
Lawyers for Sgt Nightingale will be lodging an appeal against his conviction and sentence later this week, as well as applying for bail, they said.
Simon McKay, from McKay Law Solicitors and Advocates, said: "Although unusual, an appeal against a guilty plea is permissible in English law, the test being whether the plea was a true acknowledgement of guilt.
"In this case the defence case is that Sgt Nightingale's guilty plea was not.
"As an alternative, the defence case is that the sentence imposed on Sgt Nightingale was manifestly excessive.
"I am working with William Clegg, one of the country's foremost criminal QCs.
"An application for bail will be made on lodging the appeal documentation."
The case will be debated by MPs, and four special forces veterans, including the former commanding officer of the SAS, have also written an open letter to Mr Cameron, claiming Sgt Nightingale was "the victim of a monstrous miscarriage of justice".
Sgt Nightingale pleaded guilty to illegally possessing a 9mm Glock pistol which had been packed up and returned to him by colleagues after he had to leave Iraq in a hurry to help organise the funeral of two friends killed in action. He also admitted possessing ammunition.
The court martial heard that the gun was a gift from Iraqi soldiers he had been helping to train, but the father-of-two, who had suffered medical problems affecting his memory, said he did not remember having it.