It wasn’t supposed to be like this for Rishi Sunak.

At the start of the year and after just two months in the job, he was still enjoying life as prime minister.

At a drinks reception for journalists shortly before Christmas, he had joked about already outlasting Liz Truss in No.10, while poking fun at his own diminutive stature.

“We’ve gone from the shortest-serving prime minister to the shortest prime minister,” he quipped.

When parliament returned at the start of January, he felt emboldened to make five promises on which he said voters should judge his government.

“No tricks, no ambiguity – we’re either delivering for you or we’re not,” Sunak declared.

“We will rebuild trust in politics through action, or not at all. So, I ask you to judge us on the effort we put in and the results we achieve.”

As MPs return to Westminster on Monday, the optimism of those early days has given way to cynicism and a growing sense of resignation among many Tory MPs that the party is heading for inevitable defeat at the next election.

This is despite a summer of frenetic government activity which was aimed at getting the Tories back on the front foot and eating into Labour’s huge poll lead.

Whole weeks were given over to specific topics, such as the NHS and crime, with a series of announcements rolled out in an attempt to seize the news agenda.

However, the failure of this strategy was typified by “small boats week”, which was overshadowed by Tory deputy chairman Lee Anderson telling migrants to “fuck off”, the number of asylum seekers crossing the channel hitting 100,000 and the Bibby Stockholm barge being evacuated after legionella was found in the water.

The end result has been, if anything, a hardening of Labour’s poll lead.

In a further blow to the prime minister, his communications director, Amber de Botton, surprisingly quit yesterday after less than a year in the job.

“We’re just going to have a very tough year,” one former cabinet minister told HuffPost UK.

“A lot of our MPs, the ones who were elected after 2010, are just not accustomed to it. We’ve been 20 points behind for a long time and the reality is that at least 100 of them are going at the next election, and possibly 200. We could be down to just 150 MPs.”

A veteran Tory backbencher said many of his colleagues are in for a rude awakening when they start properly engaging with the electorate.

“Judging by the MPs’ WhatsApp groups, a lot of them have spent the summer not campaigning at all,” he said.

“When they wake up and go to people’s doors and they say they’re not going to vote for them, that’ll be a reality check. That’s when things will get quite turbulent for the PM.”

Also looming on the horizon is the Mid-Bedfordshire by-election, which could take place the day after the Tories’ annual conference closes in Manchester.

Although the Conservatives hold the seat with a majority of nearly 25,000, the controversy surrounding the departure of its former MP Nadine Dorries, allied to the unpopularity of the government, means it is vulnerable.

Labour and the Lib Dems both fancy their chances, raising Tory hopes that they could split the vote and let their candidate, Festus Akinbusoye, come through the middle to win.

One senior party figure who visited the seat last week said: “Labour and the Lib Dems are knocking hell out of each other.

“The reception on the doorsteps was strikingly positive for Festus, just because they all recognised him. But it will get more difficult for him once the by-election campaign properly starts.”

Sunak’s decision to delay his long-anticipated cabinet reshuffle until later in the year has also dismayed many Tories, who believe it is a sign of the PM’s weakness.

He was forced into a mini shake-up on Thursday by the resignation of defence secretary Ben Wallace, but the decision to replace him with Grant Shapps just added to the sense of gloom in the Tory ranks.

“It’s completely lacking any inspiration – or maybe Grant was simply the only one who answered his phone,” said one unhappy aide.

“It just feels a bit like we’ve given up. The crime week announcement that we expect the police to solve crime cemented it for me. It’s a bit like telling teachers to teach kids – no shit Sherlock.”

Sunak’s malaise was summed up by polling by Redfield & Wilton Strategies for the Politico website which showed that two-thirds of voters believe Sunak has achieved either “nothing at all” or only “a slight amount”.

One veteran Tory told HuffPost UK: “My view is that because inflation hasn’t come down enough and because the NHS strikes are continuing, there is a sense among voters that there is a lack of progress.

“The good news is that inflation has actually fallen down the list of voters’ priorities recently, but the bad news is that the NHS and climate change have moved up, which doesn’t help us help at all.”

As the first anniversary of Sunak’s time in No.10 approaches, there is little to suggest he will turn around the Tories fortunes in time for next year’s general election.