“All political parties die at last of swallowing their own lies,” the Scottish physician and polymath, John Arbuthnot, once wrote. Is that what’s happening to Hong Kong’s pan-democrats?

There used to be a time when they were seen as a meaningful opposition force to counter some of the shoeshiners, sycophants and rubber stampers in the pro-establishment camp that has always dominated the city’s legislature. Not any more.

Not only are they becoming more irrelevant and ineffectual by the day, they seem to be plumbing new depths of political farce and buffoonery. Just look at the circus that has been dubbed “Staplegate”.

I’m talking about the way they handled the case of Democratic Party member Howard Lam Tsz-kin, who shocked the city with his sensational story about being kidnapped and tortured by mainland agents operating outside their jurisdiction.

Lam claimed he was snatched by Putonghua-speaking men from a busy street in broad daylight, bundled into a van and taken to an unknown location where they punched staples into his legs before dumping him on a beach last week.

It was, according to him, punishment for planning to send a signed photograph of soccer star Lionel Messi to the wife of the late mainland dissident, Liu Xiaobo.

Lam has been charged with misleading police after his story unravelled during their investigation and the case is now in court, so the less said about it, the better, until a judge determines whether he made it all up.

What is definitely worth talking about is how it has left the pan-democrats with egg on their faces and their credibility in tatters.

They threw common sense and caution to the wind in their eagerness to maximise the political mileage they saw in Lam’s story, starting with the Democratic Party holding a press conference to parade him – staples and all – in front of the media cameras before even reporting the case to police.

The luminaries of the pan-democratic leadership, including heavyweight lawyers, were quick to jump to conclusions about a further erosion of Hong Kong’s autonomy and a death knell for the “one country, two systems” policy.

Some of them made quantum leaps into ludicrous conspiracy theories, linking Lam’s case to the “co-location” controversy.

That’s the other ongoing political circus over plans to set up a joint immigration and customs checkpoint at the West Kowloon terminus for the high-speed rail link to Guangzhou.

‘Joint checkpoint deal opens door for Beijing to quash protests on Hong Kong soil’

While this sort of arrangement is perfectly normal the world over when it comes to facilitating cross-border travel, the mere thought of their mainland compatriots exercising any sort of jurisdiction on the Hong Kong side, even in a closed zone officially leased to them, unhinges our doughty pan-democrats.

Their ranks in the Legislative Council have been decimated by the disqualification of colleagues who mangled or distorted their lawmaker’s oaths and have only themselves to blame for misguided political grandstanding.

Will pan-democrats’ scare tactics and threats still work as Carrie Lam makes her mark?

Instead of strategising to regain lost ground and win back the vacant seats through impending by-elections, they’re busy crying wolf and complaining about Communist Party monsters under their beds.

People are tired of the same old narrative and negativity. Just look at the dwindling turnouts at pro-democracy rallies that once used to draw massive crowds.

We need a credible and competent opposition camp in Hong Kong, to keep a check on the government and its cronies. Not this hysterical bunch stapling themselves in the foot.

Yonden Lhatoo is the chief news editor at the Post