The Conservative Party has been fined £17,800 by the Electoral Commission for "failing to accurately report a donation" that paid for the refurb.

Labour says new information revealed by the commission suggests the PM lied to his own standards adviser about how the work was funded.

The party is calling for a fresh investigation into the PM's conduct.

Prime ministers get an annual grant of £30,000 to spend on the upkeep of their publicly-owned living quarters - but Boris and Carrie Johnson are reported to have spent as much as £200,000 on a designer upgrade.

The work was initially paid for by the Cabinet Office, but £52,000 was given to the Conservative Party by Tory peer Lord Brownlow to cover the bills. Mr Johnson says he has now covered all the costs out of his own pocket.

In May, the PM's independent adviser on standards Lord Geidt cleared Mr Johnson of a conflict of interest over the donation from Lord Brownlow, saying the PM appeared not to be aware of the arrangement with the peer.

But Lord Geidt did conclude Mr Johnson had "acted unwisely" by not being more "rigorous" in finding out who paid for the refurbishment.

On Wednesday, the Electoral Commission fined the Conservative Party for failing to accurately declare the £52,000 donation from Lord Brownlow.

Director of regulation at the commission, Louise Edwards, said the party's decisions and actions "reflected serious failings".

In response, a Conservative spokesman said it was a "technical breach" of the law and the party was considering appealing the ruling.

A number of prime ministers have chosen to live in the flat above No 11 instead of No 10, as it is bigger

Documents released by the Electoral Commission show that Mr Johnson sent a WhatsApp message to Lord Brownlow in November last year to ask for extra money to go towards the works.

Labour's deputy leader Angela Rayner said Mr Johnson "must now explain why he lied to the British public" by claiming he did not know who paid, saying he had taken them "for fools".

Ms Rayner has written to Parliamentary Standards Commissioner Kathryn Stone to ask her to investigate whether Mr Johnson broke the ministerial code and the MPs' standards rules.

"What is most concerning for me is the prime minister has lied to his own independent advisor, who found that there was no misconduct because he was given false information," she said.

The prime minister's official spokesman said Mr Johnson had "acted in accordance with the rules at all times" and "had made all the necessary declarations".

Asked explicitly if Mr Johnson had lied to Lord Geidt, the spokesman said: "No."

Downing Street maintains that the prime minster was "not aware of the underlying details" of the donations, when asked about the apparent discrepancy between what he told Lord Geidt and what the Electoral Commission has said.

Mr Johnson thought Lord Brownlow was overseeing the money, but he did not realise the peer was providing the money, as it was organised via a blind trust, his spokesman said.

Invoices paid

Publishing its findings on Thursday, the Electoral Commission said Huntswood Associates Limited - whose director is Lord Brownlow - transferred £67,801.72 to the party in October 2020.

The peer told the Commission while £15,000 went towards covering an event, the remainder went to the Cabinet Office, who had paid three invoices over the summer, totalling £52,801.72, for the refurbishment of the private residence at 11 Downing Street.

Lord Brownlow also paid a number of additional invoices relating to the refurbishment directly to suppliers, totalling £59,747.40 - making the total cost of the works £112,549.12.

The Conservative Party declared the £15,000 event donation in its quarterly donation report to the Commission, but left out the other two sums for the refurbishment.

The watchdog concluded the £52,801.72 should have been declared accurately - rather than as a loan or as part of a trust.

The direct payments to suppliers did not need to be declared, as there was no evidence the party would pay him back or that the sum was covering costs already met by the Tories.

But it criticised the party's accounting records connected to the whole incident.

As a result, the Conservatives were fined £16,250 for failing to accurately report the full value of the donation from Huntswood Associates and £1,550 for contravening the requirement to keep proper accounting records.