Uxbridge and South Ruislip may be just one parliamentary seat out of 650 – but the by-election there this month holds a much greater significance for the futures of the two main parties.

For the Conservatives, holding the seat recently vacated by disgraced former prime minister Boris Johnson, would help Rishi Sunak calm increasingly jittery backbenchers.

He enjoyed a majority of more than 7,000 and as a key outer London seat, it’s exactly the kind the party needs to win to have any hope of another term in government.

For Labour, taking Uxbridge would demonstrate the party can win back the sort of constituency that slid out of view under Jeremy Corbyn. But victory is nothing like a given – Uxbridge has its own local issues, it is relatively affluent, and Sadiq Khan’s Ultra Low Emissions Zone (Ulez, a scheme introducing a daily charge for older, more-polluting vehicles) is a divisive issue in this commuter-belt constituency.

But if Westminster watchers are excited by the high stakes contest on July 20, the constituency itself seems to have barely registered it. A few weeks off polling day, you would struggle to know there was a contest – most windows lack posters, the morning commuters were unbothered by leafleteers, and the voters don’t seem too animated about their place on the national stage.

And it’s not that Uxbridge seems too well off to be bothered. The town centre, which sits in zone six, at the very end of two Underground lines, maybe bustling on a sunny day, with mid-priced chain restaurants doing a brisk weekday lunch service. But there are also signs of tough economic times: the street is peppered with empty and recently-closed shop sites, and a food bank van makes collections from the businesses.

If the by-election is failing to set local pulses racing, the same might be said the supposed huge personal brand of their departing MP. Conversations with workers and café-goers did not suggest local indignancy about the parliamentary report on Mr Johnson that triggered his resignation. Instead most seemed to be hoping for a good local MP.

Rather than Westminster intrigue, it is issues like the cost of living, the possible closure of the local police station, the state of the NHS – and perhaps above all, the extension of the Ulez (Ultra Low Emission Zone vehicle charging scheme) to Uxbridge and Hillingdon, that they are most bothered about.

This, more than anything else, is what is giving the Conservatives some degree of hope that they might just hold the seat. One well-connected source in the party set out the overall strategy for the seat.

“The campaign message has been straightforward: talk about nothing but Ulez, drop Sadiq in whenever possible, don’t mention Boris,” he said. “So far it’s going decently on the doorstep but no one knows if it’s really going to tip the balance.”

Pressed for a prediction, though, the insider was not confident. “We’re throwing everything we have at it. But even the most optimistic London MPs feel in their hearts Labour are almost certain to win.”

But evidence that the Tories are chucking the kitchen sink at the contest seems thin on the ground in the actual constituency. At the Uxbridge Conservative & Social Club, the foyer displayed posters reminding members to pay a £1 guest fee for any non-members, listing a quiz night on 1 July, and a meat raffle to go with it. Absent was any mention of the forthcoming election.

After pressing the guest buzzer three or four times, a staffer emerged, eventually sadly concluding “there isn’t anyone here to talk to” about the election. Asked what he thought about it as he walked back to the tap room, he merely gave a half shrug.

Labour has sent Shadow Cabinet ministers and prominent MPs almost every day of the campaign in an almost frenetic bid to secure a valuable trophy. But, despite Tory pessimism, it is far from certain it can actually take the seat.

“Labour needs to be picking up new voters to win Uxbridge,” explains Ben Walker, the co-founder of @BritainElects, the UK’s largest poll aggregator and a Labour councillor himself. “They underperformed in the 2022 locals – the Tory councillors are rather popular there – so can’t rest on just their base holding firm.

“Ulez could f**k this up. Uxbridge isn’t London-London. It’s one of the most motorist seats in greater London. Campaign on a single issue of ULEZ and I suspect Uxbridge voters would split on it… it could depress Labour’s chances with new voters, meaning their win might not be as great as my forecast implies.”

A recent unannounced visit to the constituency by Labour leader Sir Keir Starmer and shadow chancellor Rachel Reeves highlighted both the party’s hope of winning and the fact that they could yet miss out.

The spectacle of this kind of political visit – this was taken with their by-election candidate, Danny Beales – is well worth watching should you ever get the chance. A handful of politicians try desperately hard to look as if they are having a normal conversation as a gaggle of advisers – shuffling out of shot – guide them where to go and try to steer people to talk to them.

Starmer received a largely positive reception – people queued up for selfies, one man shouted “good luck Sir Keir!” and a few people stopped to raise problems with him, getting their numbers taken with promises someone would be in touch.

That good reception wasn’t universal, though. After an adviser carefully positioned the gaggle of politicians so that the “Uxbridge” sign would be nicely in shot behind them, a woman ran in front of them and theatrically and noisily retched just as the photo was taken – shouting something triumphantly but inaudibly as she ran off.

Other moments were nearly as awkward. Starmer kept trying to introduce voters to Mr Beales – it’s a campaigning truism that people are more likely to vote for someone they’ve met, however briefly – but some of his introductions were downright odd.

“As we put the nail in the coffin of Boris Johnson, he’s going to be your next MP,” one non-plussed woman was told as she shook hands with the Labour candidate.

Still, most present were none the wiser. “No one knows who he is, they just want a selfie anyway,” one young man told his friend. But after someone nearby said it was the leader of the Labour party, he brightened up.

“Oh,” he said. “So can he help with the Ulez then?”