Over the almost six months of Partygate, the same narrative has played out repeatedly: just as Boris Johnson seems to have put the saga behind him, new images emerge to refocus everyone’s minds, with a corrosive effect on the prime minister’s image and ratings.

Last Thursday when the Metropolitan police inquiry formally closed with just one fine for Johnson, Conservative MPs were exchanging admiring – or in some cases exasperated – messages about how the “greased piglet” had slipped free yet again.

There was still the full report to come from the senior civil servant Sue Gray. But supporters of the prime minister were clear – a single fine for a brief appearance at an impromptu birthday celebration did not merit a leadership challenge. Time to move on.

The Daily Mail headline on Friday shouted: “What a farcical waste of time and £460,000.”

Just three days on, photos showing Johnson in a packed room raising his glass and making a speech during the leaving drinks of the former communications chief Lee Cain on 13 November 2020 make the prime minister’s life difficult again in several interconnected ways.

Even after Gray submits her report, Johnson faces an inquiry by a committee of MPs into whether he misled the Commons when he said he knew nothing about social gatherings – an offence which, if demonstrated, would normally lead to resignation.

The photos notably weaken Johnson’s defence, not least given a parliamentary exchange from last December in which the prime minister, when asked by the Labour MP Catherine West about events on the date in question, insisted “the rules were followed at all times”.

More widely, photos and other images seem to resonate with voters in a way that even repeated descriptions of suitcases of alcohol being wheeled into No 10, and Wilfred Johnson’s swing broken by drunken revellers, do not.

The first time Johnson took allegations of lockdown breaking with full seriousness was in December, when ITV News obtained footage of No 10 staff joking about an apparent party while rehearsing for planned televised press briefings.

The photos appear to weaken Johnson’s defence of rules ‘being followed at all times’.

That same evening, the video was being mocked on I’m a Celebrity … Get Me Out of Here!. The next day, Johnson’s press secretaryAllegra Stratton tearfully resigned for her role in the video, while the PM hurriedly said he was “shocked” at what it showed.

While the following weeks brought considerably more, highly detailed descriptions of what had taken place at the event joked about by Stratton and colleagues, and a series of other occasions, events took a new impetus with the release of another resonant image.

First published by the Guardian on 19 December, the photo of Johnson and more than a dozen No 10 staff sitting in the Downing Street garden on the evening of 15 May 2020 along with wine bottles and a cheese platter reimprinted events on the public consciousness.

It is testament to the power of a single, slightly grainy photograph that even though police decided not to investigate that particular gathering, seemingly on the basis it could constitute a work meeting, the idea of “wine and cheese” remains central to many people’s recollections of the perceived wrongdoing.

Unsurprisingly, polls tracking Johnson’s approval ratings notably fell more steeply into the negative around the time the video and picture came out.

The worry for Johnson is that even if he evades any more official punishment, the latest damaging images will further hit his reputation, potentially leading the Conservatives to lose byelections taking place next month in Wakefield and in Tiverton and Honiton.

A prime minister mired in scandal is one thing, and arguably not entirely unexpected for Johnson. But his MPs may be less forgiving if they believe he is becoming an electoral liability. And one thing seems certain: the pictures of Johnson holding a glass aloft will be heavily used in Labour and Lib Dem leaflets.