Imagine: Placido Domingo - The Time of My Life, BBC One

How old Placido Domingo? Old Placido Domingo in not bad vocal health, to paraphrase Cary Grant's celebrated telegram reply. The other answer depends on your source of reference. Domingo is 68 in the eyes of last night's rather lazy, over-reverent Imagine, but 75 according to my not so New Everyman Dictionary of Music. Where did that come from?

It would make him an octogenarian by the time of the date he proudly announced at the programme's end as the furthest-forward in his singer's diary. Perhaps this isn't that much of an issue. There are plenty of others that Alan Yentob might have raised here but didn't.

What's clear, and well expressed by Daniel Barenboim if somewhat vaguely and cloyingly by a vacant-looking Franco Zeffirelli and showman Zubin Mehta, is that Domingo has never lost that superabundant vitality and total identification with a role. Before I begin to sound like one of those interviewees, or Yentob himself, I ought to add that the best proof is in the live clips we saw here. Domingo has always given much more on stage than in the recording studio, so it was involving to see old footage of his velvet-to-steel Don José in Carmen under Carlos Kleiber - the only extended excerpt, of the Flower Song - and his Covent Garden Otello in agonising close-up rather than the dubbed (and abridged) Zeffirelli version. There was also just about enough of Ernani to tell us why he would have been hailed as a worthy Verdian tenor on his 1969 Milan debut in the title role.

Surely more shattering operatic events have happened in recent decades than the - o, meraviglia! - synchronised Tosca live in locations around Rome. It was a fine achievement, but from the way Yentob (who managed to tell us he was head of BBC Two at the time) talked about it, you'd think that the whole project had discovered a musical holy grail.

Domingo began to get interesting as he recalled cracking around a G natural or an A flat when he started singing Wagner's Lohengrin at the age of 27. He laid the blame on over-coaching. Why? If Yentob asked, it didn't survive the editing process. Nor were any questions raised of the once-perceived failure to hit the Pavarotti jackpot of the golden top notes, or any details given of why or how Domingo progressed from baritone to tenor and is now, as Verdi's Simon Boccanegra, moving back down again (though again Barenboim came briefly to the rescue with a little chapter and verse).

The spadework on Domingo's early years in Spain and Mexico was decent enough, and it was good to hear how accomplished his mother was as a singer of the Spanish light-opera form known as zarzuela. There was a charming sequence in which his sons, including Placi Domingo the Third, all participated in karaoke. His involvement in the Mexican earthquake, launched by personal tragedy, seems as admirable now as it did in 1985. And the launch of the Operalia festival for younger singers surely stems from the best of motives. Yet once again Yentob had to go and spoil it all by flashing back 50 years to the young Domingo's appearance with the veteran Lily Pons and affecting a certain wryness as he said to Domingo, "I sense from that moment you felt the need to pass the baton on."

I sense nothing of the sort. It's needling to be put on the defensive by such a hagiographic approach. Because it probably is true, after all, that no tenor has ever acted with such ferocious intensity combined with handsomeness of stage presence. "Placid Sunday", as the show wasted no time in telling us the name translates, he never has been, and never will be; but this programme was about as placid Sundayish as they come.

Domingo sings The Flower Song from Carmen:

• Watch Imagine: Placido Domingo on BBC iPlayer