It is alleged the arrangement for Gina Coladangelo – whose embrace of the former health secretary breached Covid regulations, forcing his resignation – broke the rules because she was not working for the peer.
Lord Bethell, a close ally of Mr Hancock, was already facing calls for his dismissal over his use of private emails for official work, something No 10 first denied and then admitted.
Now the Lords Commissioners for Standards has announced that the minister is under investigation over his “use of facilities” in relation to Ms Coladangelo.
A House of Lords spokesperson confirmed the probe centred on a “complaint regarding Lord Bethell sponsoring a pass for Gina Coladangelo”.
Peers are allowed to sponsor passes for secretaries and research assistants, but only if they “genuinely and personally” fulfil those roles for him or her, signing a declaration to that effect.
Passholders enjoy free access to the Palace of Westminster, where they can mingle with ministers and MPs and use the estate’s facilities such as bars, restaurants and a gym.
Lord Bethell has also been in the spotlight for appointing the head of Portland – the lobbying firm he used to work for – as an unpaid media adviser, taking part in daily strategy calls.
Meanwhile, Lord Feldman, the former Tory party chairman turned lobbyist, was secretly made an adviser on procurement, helping to secure a government contract for a client of his own company.
Ms Coladangelo, a long-time friend of Mr Hancock, was made his unpaid adviser before being appointed as a £15,000-a-year non-executive director at his department.
The pair were caught embracing on leaked CCTV footage. Mr Hancock resigned a day later, despite Boris Johnson giving him a vote of confidence.
Ms Coladangelo is no longer listed as a member of staff for Lord Bethell on his parliamentary web page.
But an online archive showed she was listed as a staff member in May last year as “Mrs Gina Tress”, a marketing and communications director for Oliver Bonas – the retailer founded by her husband, Oliver Tress.
Last month, leaked minutes showed a top health department civil servant had warned about both Mr Hancock and Lord Bethell’s use of private emails for government business.
The peer “routinely uses his personal inbox and the majority of [approvals for contracts] would have been initiated from this inbox”, the documents obtained by The Sunday Times revealed.
Official guidance states that all “substantive” government information must be “accessible” by, for example, “copying it to a government email address”.
The Information Commissioner, Elizabeth Denham, has revealed she is weighing up an investigation, arguing there is genuine public concern that vital information was concealed.
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