Let's hear it for the understudies, alternates and swings – keeping our theatres in action

In this era of Covid-positives, disrupted press nights and perpetual turbulence, never before has the pragmatism, audacity and skill of theatre professionals across the land been more evident. Even after the shift in government restrictions (the rules changed in August so that an entire company is no longer forced to isolate if a single positive Covid case was found), producers and cast members have gone above and beyond to make sure that, after such a long time waiting – the show will go on.

One example was the recent revival of Constellations where, with Anna Maxwell Martin off ill, Chris O'Dowd and Omari Douglas reimagined the two-hander, having never rehearsed the 75-minute play together. Quite literally stellar. Over at Hairspray, producers went as far as to cast an entire second ensemble in the event that one group is forced to isolate. The Royal Court relocated an entire production due to flood damage. These are just the anecdotes from a caffeine-deprived brain the night after a West End opening.

But one experience really brought it home yesterday as Mark Oxtoby stood in for an absent Roger Bart who, for Covid reasons, was forced to skip the London opening of Back to the Future the Musical. As producer Colin Ingram highlighted as he took to the stage during the curtain call, Oxtoby had never done a live performance to a Back to the Future audience, never done an understudy run and was coming in as fresh as could be.

But theatre professionals are the best of the best and, even with the original Doc Brown Christopher Lloyd watching on, he delivered what was an assured, hilarious, bumbling and endearing turn. As anyone who has seen it will know, this is a mighty, technical challenge, and Doc Brown has a fair few numbers to blast through over the course of the chronological caper. Given Bart voiced the character of Hercules, it's only right that what Oxtoby did was downright Herculean. Special praise must also go to the musical director, directors, backstage team and fellow cast members, who all made the actor's first appearance seem seamless.

If the theatre world eventually returns to pre-pandemic audience numbers, it will not just be because of starry big names drawing in the punters, it will be off the back of those who have lost so much over the last 19 months through lack of sustained government support – the freelancers who have returned with downright heroism.

It is through their efforts that shows go on, ticket holder plans aren't disrupted and nights aren't wasted. Everything needs to be done to keep spectator confidence high, and understudies, alternates, swings and company members, such as Oxtoby are playing an incredible part.