Officials have been asked to explain why Kwasi Kwarteng’s notorious champagne reception with bankers wasn’t listed on his published diary.
The former chancellor was reported to have attended a reception with hedge fund managers and people working in financial services on Friday 23 September - just hours after delivering his disastrous mini-budget.
The Times reported the event took place at the Chelsea home of Andrew Law, a Tory donor.
And it was claimed attendees who would stand to gain from a crash in the pound “egged him on” to stick by his bonkers economic plans.
Lib Dem Cabinet Office Spokesperson Christine Jardine said: “The Conservatives crashed the economy and as a result Kwasi Kwarteng will go down as one of Britain's worst Chancellors.
“What’s worse is that in the aftermath of this destruction, we are still not getting the transparency we deserve regarding Kwarteng’s champagne party held with top bankers on the day of the Budget.”
Ministerial meetings are supposed to be declared quarterly - with a list of attendees.
The government dumped 122 files on its website on Thursday - the last Commons sitting day before Christmas.
But there was no record in the Treasury’s disclosures of the event - or who enjoyed cocktails and fizz with the Chancellor.
Ms Jardine today wrote to Cabinet Secretary Simon Case demanding an explanation.
She added: "We need an inquiry into this immediately to establish the facts. More than ever we also need an independent ethics advisor to keep tabs on this Conservative Government, which has shown time and time again it is one rule for them and another for everyone else.”
Mr Kwarteng later accepted, that “with hindsight it probably wasn't the best day to go".
"I spent, I think, quarter of an hour there, or maybe a bit longer. It was a party event, we have party events all the time,” he said.
"I think it was a difficult call and I totally get how it looks. I just feel that it was something that I was signed up to do and I had to do."
The Treasury said ministerial rules required any government business that took place at the meeting to be fed back to officials.
A Treasury spokesperson said: “HM Treasury regularly publishes information about all official meetings to comply with transparency requirements.
"Non-government meetings, such as party political events, are not required to be published.”
