It was a day of the bicycle, real and imaginary, in Dublin, where popular protest and purple prose combined to elevate the humble velocipede to greater than normal prominence.

First there was a mass demonstration in support of safer cycling conditions on the city quays. Then the scene shifted to the annual commemoration of Brian O'Nolan, aka Flann O'Brien and Myles na gCopaleen: a three-speed writer who created some of the weirdest and most famous bicycles in literature.

This year's Mylesday marked the 50th anniversary of O'Nolan's comic masterpiece The Third Policeman (written under his Flann O'Brien hat), which he never saw published, having died 51 years ago, on April Fool's Day 1966.

The book is an existentialist murder mystery set mostly in eternity. But thanks to recent events back in real-world Ireland, it has never seemed so realistic as it does now.

A major subplot of the novel, after all, is the falsification of crime statistics by a group of outlandish police officers who, supposedly for health and safety reasons, keep hiding people’s bicycles and then finding them again.

The book was written as a follow-up to his similarly quirky 1939 debut At Swim-Two-Birds. And as poignantly recalled in The Palace Bar – Mylesday headquarters – publishers rejected it then because they thought "he should become less fantastic, and in this new novel he is more so".

Somehow, the plot doesn't seem quite so fantastic today. Readings in The Palace also included several on another of his favourite subjects: alcohol abuse. So perhaps had he been encouraged to write a sequel to The Third Policeman, Flann O'Brien's wild imagination would eventually have created something like the million fictional breathalyser tests too.

As it was, Sunday's events featured an unintentionally satirical twist of which Myles na gCopaleen, his pseudonym for the long-running Cruiskeen Lawn column in The Irish Times, would have been proud.

It turned out that the several hundred cycling campaigners who had gathered earlier in the Phoenix Park were equipped not just with bells, but with quite a few whistles too. This was for the standard protesters’ practice of making noise, and was in no way intended as a commentary on recent news events in Irish policing.

Even so, if you had nodded off on night duty at nearby Garda HQ, the accumulation of whistleblowers in the area might have seemed like a Sunday morning nightmare come to life.

In fact, the main focus of the demonstration was Dublin City Council and the need for a dedicated Liffey Cyclepath on the congested quays. And as leaders of the Dublin Cycling Campaign pointed out, there was a very serious reason behind it.

Already this year, five cyclists have died on Irish roads, including three in Dublin. This was a "horrific" statistic, said DCC chair Colm Ryder, but there were also multiple near misses, including "people being knocked off their bikes regularly", because of poor infrastructure.

The peloton of protesters proceeded at a stately pace along the north quays, attracting some friendly beeps from motorists and also a few angry ones from those impatient of even slight delays.

It passed, among other places, the Custom House, where O’Nolan was long based in his day job as a civil servant. And aptly, the cyclists paused there for a moment’s silence, although that too was inadvertent. They were only waiting for the lights at Matt Talbot Bridge to change.