Here is the scene on an otherwise fine Glasgow evening in the early spring of 2013, described by those who felt embarrassed to have been there.

Firhill Stadium in Maryhill, where the under-17s of Rangers and Celtic are meeting in the Glasgow Cup Final. There is much anticipation of this game - it might otherwise have been ignored - given that Rangers and Celtic no longer meet on regular league business and hadn’t played each other for a year.

The small stadium is pretty packed: 6000-plus turn up. But it quickly turns sour and ugly in the time-honoured Old Firm way.

The old unsavoury songs from both sets of supporters are soon filling the air. Some seats are ripped up. Smoke-bombs are let off. The stewards and the police - the latter of whom were under no illusions about potential trouble - are soon being exercised.

“The loutish behaviour and sectarian undercurrent hasn’t gone away,” wrote the football reporter, Scott McDermott, who attended the match.

Down on the pitch you’ve got 16 year old kids playing football for Rangers and Celtic. Noticeably, in the stands, there is also a heavy preponderance of youth among these Old Firm fans, who nonetheless appear well acquainted with the uglier, more ancient sentiments.

One particular photograph of the occasion appeared to show a teeming section of the crowd with scarcely anyone older than 18 in the frame.

It was a depressing episode in Glasgow on Monday night. Time and again, in part to try to sound upbeat after years of doomsaying, I’ve tried to assert that “bigotry and the Old Firm” is getting better, is improving. Yet time and again these incidents spring up.

Strangely, this wasn’t the first time in recent years that a “colts” Old Firm match had become the setting for that exotic mix of sectarianism and yobbishness.

At the Scottish Youth Cup final between Rangers and Celtic at Hampden in April, 2011, both sets of fans were filmed by police singing sectarian songs. On that occasion, just like this week, witnesses at the game were taken aback that a youth fixture could produce such bile.

Monday night in Glasgow will soon fade into the background - all these “unsavoury occasions” do after a few days of tut-tutting. But what do such scenes tell us about where we are going with bigotry in Scottish football?

It's a complicated issue. There seemed little doubt that, in considering a wider body of recent evidence, behaviour at Old Firm games had got better.

In part due to laws which effectively tried to ram better behaviour down idiots’ throats, the atmosphere at matches had improved.

There does, though, seem to be a fresh generation of Rangers and Celtic supporters who revel in the old ways of dire behaviour.

Firhill - both from pictures and from the bulletins of those who were there - appeared to be filled with younger supporters who were singing stuff that embarrassed Rangers and Celtic in the 1970s.

This fits with a regrettable recent trend, which suggests that, either via father-son relationships, or peer pressure, the internet or whatever, sectarian slogans are finding a fresh berth among younger fans.

One other truth seemed obvious from Monday’s incident - most Old Firm fans badly miss the Glasgow derby following Rangers’ liquidation and will flock to anything that as near as resembles it.

There is a fondness among some Old Firm fans - which I don’t believe - for claiming that they don’t miss Rangers-Celtic games at all.

In part, this is a protective mask worn by Rangers fans, who wish to disavow any bitterness or anger on their part, or by Celtic fans who want to deplore any suggestion of life being less exciting without their rivals.

Much of this is a game of point-scoring. In truth, most miss the Old Firm game badly, warts and all. In fact, many miss it, most especially for its warts and all.

Some repeatedly say: don’t read too much into events such as Monday at Firhill, and there is a natural truth in this. We’ve all learned that you cannot - you should not - take a football-related incident and duly connect it to a sweeping statement about wider society.

Nonetheless, Rangers and Celtic and delinquent behaviour remain a vexing ménage a trois. Even at a youth game, alas.

This poison still needs extracted, despite what many like to claim.