A review published today says London City Hall's code of conduct must be bolstered following a probe into Boris Johnson's links with an American businesswoman while mayor.
Jennifer Arcuri's links with Mr Johnson came under scrutiny over allegations she received favourable treatment for her business ventures during his eight-year stint leading the capital.
The former London Mayor avoided a criminal investigation after the Independent Office for Police Conduct found no evidence he influenced the payment of thousands of pounds of public money to Ms Arcuri, or secured her participation on foreign trade trips that he led.
In a report, a cross-party group of Assembly Members recommended the code be updated to ensure that any Mayor or Assembly Member should be in no doubt that they should declare non-pecuniary interests such as personal relationships with individuals.
It comes as MPs investigating whether Boris Johnson misled Parliament over Partygate yesterday rejected a claim their probe is "unfair" and "fundamentally flawed".
A committee is set to quiz the ex-Prime Minister this autumn over his statements to the Commons relating to lockdown-busting parties in Downing Street, first revealed by the Mirror.
A legal opinion commissioned by the Government from senior barrister Lord Pannick KC shortly before Mr Johnson quit No10 warned the investigation by the Commons Privileges Committee would be ruled unlawful by the courts.
But in its response, the committee said its legal advisers believed Lord Pannick's opinion was founded on "a systemic misunderstanding of the parliamentary process and misplaced analogies with the criminal law".
It rejected his view that a fair procedure would allow Mr Johnson to be represented at its hearings by counsel who would be able to speak on his behalf and cross-examine witnesses.
It said that while witnesses were allowed to be accompanied by a legal adviser, it would require a change in the procedures of the House to allow them to take part in the hearings.
The committee also dismissed Lord Pannick's argument that a failure to make an explicit distinction on whether Mr Johnson misled MPs intentionally could have a "chilling effect" on parliamentary debate, with MPs fearful of misspeaking.
MPs insisted there were well-established ways for ministers to correct the record when the House was misled.
"The committee's resolution on procedure makes clear that there will be multiple opportunities for Mr Johnson to consider the evidence and respond to points made by other witnesses or the committee, concluding in an opportunity to comment on any criticisms included in the draft of the final report," it said.
"It is not the case that Mr Johnson would be called to give evidence without knowing the detail of the case that he has to meet.
“That is a fundamental misunderstanding of the committee's procedure."
