PM asked to halt hunger strike by Falklands hero
Squadron Royal Engineers received treatment for PTSD at the centre for many years before his support was axed three years ago.
The charity has now admitted his treatment fell “well short of accepted practice” and has pledged to review veterans' cases.
Campaigners say more than 150 ex-Forces personnel and their families have complained of failings.
On Sunday the President of Combat Stress, former head of the British Army General Sir Peter Wall, visited Gus and apologised.
Gus, from Builth Wells, Powys, wants a full independent inquiry into the “systemic failings” of the charity. He has pledged to continue his protest until Armistice Day.
Yesterday Mr Davies hit out at Combat Stress, which he says he has been lobbying on Gus's behalf after the veteran's wife Angela, 61, urged him to take up the case.
The MP said: “I am saddened Mr Hales has felt the need to take such drastic action. When I heard of his hunger strike I was in Westminster.
“I immediately arranged meetings with Mr Ellwood and contacted the Prime Minister's office.”
Mr Hales accused Combat Stress of repeatedly changing its position over Gus, adding: “If they had admitted they had not followed procedure in the first place this situation would have been avoided.”
Gus said: “Mr Davies is quite correct. If I had been taken seriously over the last three years I wouldn't be here now.
“There's an empty chair next to me. If the Prime Minister wants to sit here I'll tell her what the problems are with care for veterans.”
Leona Roberts, a member of the Falklands Islands government, travelled up from official meetings in London to visit Gus. She said: “It was incredibly moving. All British veterans are very dear to us.”
A spokeskman for the Prime Minister declined to comment.