Seven o’clock on a Monday night and I am standing in the House of Commons, nursing a glass of vinegary white wine.

All around me are people doing the same, though it’s polite sipping rather than getting sloshed. Waiters ferry bottles between the terrace function rooms, where MPs are hosting dinners or campaign launches like the one I’m at. Between the clanging division bells summoning MPs for votes that will go on tonight until gone 11pm, the Strangers’ bar is doing its usual trade.

Welcome to the working-but-not-quite-working time of night, where professional shades into slightly social; a fuzzy grey area that can sometimes get too fuzzy for everyone’s good. But it can also be a surprisingly productive time, as I realised only after having a baby for whom I needed to get home in the evenings, and realising how painfully out of the loop that made me.

For Hannah Spencer, the new Green MP for Gorton and Denton, parliament’s drinking culture was clearly a shock. “You can smell the alcohol when people are in between votes,” she told PoliticsJoe, adding that she’d have been sacked for boozing on the job as a plumber. After backlash from other MPs who found the outrage rather performative, she hit back on Instagram, arguing that MPs didn’t have “a right to get pissed at work”. All of which will do wonders for her image as an outsider bursting Westminster’s bubble. But what if she has made the classic newbie mistake of antagonising colleagues before she’s even got to know them, when she could have been building an alliance for change?

For if Spencer finds it boozy now, she should have seen it in the late 1990s: two-bottle lunches that I dreaded as a lobby journalist because I couldn’t keep up, and snoring men sleeping it off in the libraries. Thank God for an influx of mostly Labour women, who made it socially acceptable to drink fizzy water and fought to change the working hours so that they could occasionally put their kids to bed.

Spencer is right, of course, that parliament is fundamentally weird. It still looks like Hogwarts, though the mostly state-educated cabinet is the least posh for decades; the rituals remain bafflingly arcane and it’s still too tolerant of gropers and bullies. She’s right, too, that millions of people aren’t allowed to drink at work, though the dividing line isn’t straightforwardly a class one. (City boys still indulge at lunch, but not brain surgeons or teachers.) Work-but-not-work drinking is common in professions where information is currency and booze loosens lips, or else helps everyone forget that this is now a 12-hour day for which they’re not getting overtime: brokers and lawyers, journalists and PRs, publishers and politicians.

What Spencer seems to have missed, however, is the root cause of Westminster’s drink problem. Why does parliament, a place for deciding life-and-death issues, even have bars? Loneliness, stress and pack bonding under pressure are part of the answer. But chiefly it’s about being kept there late at night to vote, sometimes on momentous issues – though on those nights the bars are emptier, and the chamber full – but more often on technical amendments to legislation they’re barely following, with endless hanging about in-between. In-house restaurants and bars keep backbenchers fed, watered and where the whips can see them, while enabling after-work grousing, trading of information or the buttonholing of ministers who haven’t returned their calls.

The sight of tired people who’ve been at work for 14 hours being pushed through this legislative meat grinder, asking colleagues to remind them which way they’re supposed to be voting, isn’t always pretty. For frustrated backbenchers it can feed the feeling that they’re just lobby fodder, herded around like so many powerless sheep. Whether or not that’s true, to change the drinking culture, you need to change the reasons MPs drink.

Bring back secure, remote electronic voting – which worked during lockdown – as an option for those who want to go home at night, while allowing those who want to vote in person to do so. Reform working hours and processes so that critical decisions aren’t taken by people who should have been asleep hours ago. Create more meaningful career paths for the many MPs who will never be in cabinet but could be usefully challenging the executive, taking politics out to the public, becoming conduits for new ideas. Granted, there are fewer Instagram likes in it. But it’s how change actually happens.

• Gaby Hinsliff is a Guardian columnist