Focus have just played “House Of The King” – one of the most recognisable prog rock songs in the world – and Menno Gootjes, their guitarist, has broken a string. This means that main man, Thijs van Leer has got to fill.

He does this by merrily explaining (in fairness to van Leer everything he does could be described as “merry”) what they’ve played so far.

“We started with a flute solo,” he begins (they had) “then we played a tune called ‘Focus 1’…..now we want to play something a lot more serious…..

In practice, that means “Eruption,” a “piece” – this seems to be the best word for it – of over 20 minutes and one which is genuinely stunning. For all the smiling, for all the fun they have on the “podium”  – and it’s worth pointing out that van Leer refuses to call this a “stage”, explaining that the aforementioned “…..King” was the one that “took us from where you are and gave us a career.” – this is a band who deadly serious about one thing: and that’s the music itself.

And the four are as good as it gets. The musicianship is from the top draw, but never at the expense of the songs. It’s easy, perhaps, to do that when the music is intricate as this, and you can do what comes naturally, but its way more than that. There’s a bit in “Eruption”, for example, when van Leer does a scat section and its all he can do to stop laughing. This is mostly all about the enjoyment of the show. Nothing more and nothing less.

Elsewhere, there are some classic moments of classic rock, if you will. “Sylvia” begins in an incredibly funky fashion, but the riffs of Gootjes really shine here.

There’s a moment of poignance too, with a new track “For Bert”, played in tribute to Bert Ruiter, the band’s long time bass player, who passed away in March. Fittingly, Udo Pannekeet – the present incumbent – is magnificent here.

“La cathédrale de Strasbourg” and “Harem Scarem” are perhaps best viewed as two sides of the same coin. The former is beautifully done, the latter is heavy, harsh and “for the boys that are not spiritual at all”. This one is also a vehicle for Gootjes to play his solo and Pannekeet to do the same, but it segues into “Hocus Pocus”. The bonkers, off the wall, yodel -filled heavy progger that has been covered by artists as big as Iron Maiden. It’s brilliant, too and you can’t help but smile as they play it.

Drummer Pierre van der Linden – who has been at van Leer’s side since 1971 – plays his solo in the middle of it and it is appropriately sprinkled with magic, before the band join for a curtain call.

Van Leer had earlier claimed that there was a strict curfew at 11pm, but in the event, he seems less bothered as they encore with “Focus 3” and it stretches out in a more leisurely fashion. Unhurried, it does what it will and in its own time.

Van Leer makes his way to the front to say his goodbyes but what he said just before it finished, interestingly seems to sum things up: “thank you, we love coming here and you always make us feel like we’re home”.

Focus have been a band for over 50 years, they clearly love being on stage as much as ever, but the way they bring the audience along too is truly masterful, such warmth is rare, such skill is rarer. And if ever there was a band who deserve their celebration, its this one right here.