When corruption taints politics in other countries, British media is happy to call it was it is: corruption. But they have a special word for it when it happens in the U.K.—"sleaze." With the current government of the U.K. so baldly mired in slea—sorry, corruption— that it has begun to make international headlines, the very British euphemism itself comes under scrutiny.
Here's Patrick Gathara, writing it up the way Western media tends to write about the developing world:
Newspaper editorials are decrying "sleaze" – a catchall phrase for questionable and scandalous conduct – in the oil-rich kingdom where, since the start of the COVID-19 pandemic and despite the huge conflicts of interest, a third of MPs have pocketed nearly $7m in payments for moonlighting with private firms, including those bidding for contracts related to pandemic measures. Further, the ruling party has also been accused of selling seats in the upper chamber of parliament, the House of Lords, to donors for up to $4m.
Garatha traces a thread back to the origins of modern corruption in colonial-era Africa.
To this I would add two things: first, it has the more mundane purpose of simply telling people how they should feel about corruption in the UK: sordid yet trivial, hypocritical but hapless, pathos not worthy of punishment. The term was originally popularized in the 1990s to refer to the constant stream of sex scandals and grifts undermining the Conservative government then, and its imprecise bundling of (legal) sexual and (illegal) financial misconduct is a key feature of the meme.
Second, corruption is a crime, and England has crude, plaintiff-friendly libel laws that shift the burden of proof to the defendant. The use of vague but implicating euphemisms is simply legal op-sec for media there.
The result is as intended, then, by London's well-connected media: corruption sublimated into a profitable entertainment genre that no-one takes seriously and into an accusation that presents less legal risk. To even point out that "sleaze" is just plain old corruption means you're not getting the joke.