Dame Cressida declined to say which alleged parties are being investigated, nor would she put a timeline on when officers could detail their findings.
The gatherings were already under investigation by senior official Sue Gray, and the Cabinet Office said her work continues.
Among the number of events alleged to have taken place at No 10 was a birthday party for Boris Johnson - where interior designer Lulu Lytle was reportedly spotted.
So, when did the birthday party take place and who was invited? Here’s all you need to know.
When was the Prime Minister’s birthday party - and did Lulu Lytle attend?
It has emerged a gathering was held for Boris Johnson’s birthday in 2020 while the country was plunged into the first lockdown.
A Downing Street spokesperson admitted staff “gathered briefly” in the Cabinet Room after a meeting, following a report from ITV News which suggested up to 30 people attended.
The broadcaster suggested the Prime Minister’s wife, Carrie Johnson, had organised the surprise get-together.
Lulu Lytle, the interior designer behind lavish renovations of Mr and Mrs Johnson’s flat, admitted she “briefly” attended while undertaking work in Downing Street while waiting to talk to Mr Johnson.
Soane Britain, the luxury designer co-founded by Ms Lytle, said she was “present in Downing Street on June 19 working on the refurbishment”, which has been subject to multiple investigations over its funding.
“Lulu was not invited to any birthday celebrations for the Prime Minister as a guest,” the spokeswoman said.
“Lulu entered the Cabinet Room briefly as requested, while waiting to speak with the Prime Minister.”
ITV News also reported that later the same evening, family and friends were hosted upstairs to further celebrate the Prime Minister’s 56th birthday in his official residence.
Who is Lulu Lytle?
Lulu Lytle is the co-founder of interior design company, Soane Britain, which she started up in 1997, aged 25, and now employs 75 people.
She works with 40 workshops specialising in interior design and handmade craftmanship around Britain with clients including Soho House and Chequers - under a former prime minister.
As a student she started working in antiques and took a part time job flower arranging at Mark Birley’s private member’s club before going into business with co-founder antiques dealer Christopher Hodsoll.
In 2020, she was commissioned by the Prime Minister and Carrie Johnson to redecorate their No 11 flat.
Later, the revamp got caught up in a media storm after it emerged that it cost more than £100,00.
Reports circulated at the time that gold wallpaper - supplied by Sloane Britain - cost £840 per roll and started ‘peeling’ off the walls in Mr Johnson’s Downing Street home months after it was put up.
What was the ‘sleaze’ probe?
Calls were made for the prime minister to be investigated by Parliament’s “sleaze” watchdog into the £112,000 refurbishment of his Downing Street flat.
On 24 January, 2022, No 10 confirmed the probe would not be going ahead after Boris Johnson had failed to reveal about his exchanges with a Tory donor who helped fund the revamp.
Mr Johnson’s now wife, Carrie Symonds, 33, reportedly saw the lavish overhaul as necessary to rid the Prime Minister’s residence of the “John Lewis nightmare” left behind by Theresa May.
In May 2021, independent adviser on ministers’ interests Lord Geidt ruled that Mr Johnson had “unwisely” allowed the refurbishment of his Downing Street flat at No 11 to go ahead without “more rigorous regard for how this would be funded”.
There had been discussions about a Downing Street Trust being set up to pay for the work, which exceeded the annual public grant of up to £30,000 the Prime Minister can spend on renovations.
But this did not come to fruition, and a later Electoral Commission (EC) investigation found a total of £112,549.12 had been paid by Huntswood Associates – whose director is Lord Brownlow – to cover the work by luxury firm Soane Britain, which is owned by interior designer Lulu Lytle.
The EC said that on November 29 last year, Mr Johnson sent a WhatsApp message to Lord Brownlow “asking him to authorise further, at that stage unspecified, refurbishment works on the residence”, suggesting Lord Geidt had been misled.
In these messages, Mr Johnson tells Lord Brownlow: “I am afraid parts of our flat are still a bit of a tip and am keen to allow Lulu Lytle to get on with it. Can I possibly ask her to get in touch with you for approvals?”
To which Lord Brownlow replies: “Of course, get Lulu to call me and we’ll get it sorted ASAP!”
In a second message, he adds: “I should have said, as the trust isn’t set up yet (will be in January) approval is a doddle as it’s only me and I know where the £ will come from, so as soon as Lulu calls we can crack on.”
No 10 said describing the flat as a “tip” reflected “the fact that works were incomplete, refurbishment and renovation works were incomplete, at that point, which meant the further expenditure was necessary to complete them”.
A spokesman for the Prime Minister acknowledged that Mr Johnson got funding to decorate, and he said: “There is an annual grant for the Downing Street residences which allow for modernisation and upgrades, and ensuring that things work as they should.”
A message from the editor:
Thank you for reading. NationalWorld is a new national news brand, produced by a team of journalists, editors, video producers and designers who live and work across the UK. Find out more about who’s who in the team, and our editorial values. We want to start a community among our readers, so please follow us on Facebook, Twitter and Instagram, and keep the conversation going. You can also sign up to our newsletters and get a curated selection of our best reads to your inbox every day.