Mr Johnson has sent Miss Hossack emails praising her work
A solicitor who is facing a disciplinary panel after campaigning against a care home closure in Hull has been supported by the home secretary.
Yvonne Hossack called Alan Johnson as a witness at the Solicitors Disciplinary Tribunal hearing in London.
Mr Johnson, a Hull MP, said he backed a campaign by Miss Hossack, 53, against the closure of Rokeby House.
The solicitor, from Kettering, Northamptonshire, denies breaching rules governing solicitors' conduct.
Mr Johnson, who stressed he was speaking as a Hull MP and not on behalf of the government, said he had represented his constituents "effectively" in a battle against the closure of the care home.
Miss Hossack asked him: "Does it concern you that your constituents may be unrepresented by me at the final hearing of their case?"
Mr Johnson said: "Yes, it would concern me if my constituents were unrepresented."
And asked if it was important they had continuity, he said: "Yes."
Miss Hossack is accused of six breaches of rules governing solicitors' conduct, including accessing instructions from third parties without seeking clarification of the position and providing confidential information for third parties.
The solicitor asked Mr Johnson whether he agreed with Hull City Council when it complained that her efforts to prevent three men being moved from the home brought her profession into disrepute.
He said: "In relation to my involvement in this case, I wouldn't agree with that.
"I'm not aware of the code of honour that solicitors abide by, but as a constituency MP, representing my constituents, I wouldn't agree with that."
Mr Johnson agreed he had sent Miss Hossack emails praising her work.
In one he said he admired her work, but wished she would show less naivety over the political process.
And in another he said there was a large gin and tonic waiting for her on the Strangers' Bar in the House of Commons if she came to London.
"Are those still your views?" she asked.
"Yes," he replied.
The hearing continues.