Friends of Tory campaigner Kate Maltby fear Damian Green may escape official sanction for alleged inappropriate behaviour towards her because it took place before he was a cabinet minister.

The Guardian understands Maltby’s supporters are concerned at the possibility Theresa May’s deputy may be allowed to stay in post because he will be deemed by a Cabinet Office investigation not to have breached the ministerial code, given the events in question took place after July 2014, when he was not a minister.

Maltby, who is 30 years younger than Green, has told the inquiry she believes Green appeared to solicit sex from her in exchange for political mentoring. She declined to comment on Tuesday, with the investigation into Green set to be released in the coming days.

In an article for the Times, which prompted the inquiry, Maltby said she met Green in a Waterloo pub, where she said the MP offered to help her take steps towards becoming a Conservative candidate. She alleged that Green had touched her knee during the meeting, as he mentioned that his own wife was “very understanding”.

Maltby described a conversation that she said touched on affairs of acquaintances, then she said she “felt a fleeting hand against my knee – so brief it was almost deniable”.

The activist said she avoided Green after their encounter but, in 2016, subsequently wrote a piece for the Times where she was pictured wearing a corset. Green then texted her unprompted, she said, saying: “Long time no see. But having admired you in a corset in my favourite tabloid, I feel impelled to ask if you are free for a drink anytime?”

After the message from Green, Maltby said she did not reply but that day she privately messaged a number of friends expressing concern, including an Evening Standard journalist who published the messages earlier this month.

Green denies the allegations. After the article was published, he said the meeting was “two friends agreeing to meet for a regular catchup – and nothing more ... This untrue allegation has come as a complete shock and is deeply hurtful, especially from someone I considered a personal friend”. Maltby declined to comment before the investigation was concluded.

The inquiry into Green, who remained in post, has been since expanded to take in claims that pornography was found on his House of Commons computer when it was raided in 2008 as part of an inquiry into Home Office leaks. Green has denied accessing or viewing pornography on his computer.

On Monday, the Guardian reported that the inquiry by the Cabinet Office’s Sue Gray, the director general of the propriety and ethics team, is understood to have been asked to examine whether Green or his allies later influenced a Daily Mail article about Maltby that followed her piece accusing Green.

After Maltby’s allegations were published, she was profiled by the Daily Mail’s Andrew Pierce in a piece that called her “one very pushy lady” and said she was “determined to make it in politics – whatever the cost”.

The article, which drew significant criticism after it was published, suggested Maltby’s parents were “aghast at what she had done” by accusing Green, which she denies. It said she had a “flair for self-promotion” and was “keen to make her mark in politics”.

Maltby did not reply to Green’s text message but after he became work and pensions secretary in 2016, the pair exchanged friendly texts where Maltby congratulated him.

Several MPs expressed concern about the wider implications if the ministerial code ends up being the clinching point.

Labour MP Stella Creasy said: “For the men and women brave enough to come forward, what message would it send if the powerful close ranks rather than recognise change needs to happen?”

MP Jess Phillips, chair of the women’s parliamentary Labour party, said if Green was found not to have breached the ministerial code it would be a “weak argument about why we have a different standards to other people.”