This is an evening of pure escapist fantasy and a tease on a majestic scale, whilst being grounded in the realities of terminal illness. It is an odd mix.

89-year-old Maurice (Julian Glover) wants to reach his 90th birthday because he believes the Queen will come for tea on that day. They made a date 60 years ago. This isn’t as bonkers as it sounds – to us, and to his long-suffering wife, Helena (Gay Soper) – because Maurice used to be a jeweller and volunteered to guard the Crown Jewels the night before the Coronation.

He thus spent a couple of hours in the company of the young, beautiful, soon-to-be Queen on his birthday and fell in love with her – a love that has lingered, and impinged on his marriage, for the last six decades.

The problem is that Maurice has eight brain tumours. His nurse, the gawky, unmarried Katy (Nichola McAuliffe, who also wrote the play) tells him that he has only weeks to live. She believes in being straightforward about these things. Helena has been driven to distraction by Maurice’s obsession but colludes in the idea that Katy might impersonate the Queen to give a dying man his wish. We learn that Katy has been involved with amateur dramatics, although mostly backstage, and it seems a preposterous notion.

However, the turn she gives as Her Majesty is so compelling, and so accurate, that it seems way beyond the capabilities of an occasional am-dram costume-maker. To say more would be to indulge in spoiler tactics, but suffice to say that we are required to suspend about as much disbelief as it is possible to suspend in one evening.

It is a somewhat lop-sided script, with a plodding, meandering first act, and a tour-de-force of a second act. NMcAuliffe has written a peach of a part for herself, and she carries it off to perfection. Glover seems overly robust for a dying 89-year-old, but invests Maurice with a gruff charm and a delicacy that befits a man whose life has been spent in the company of precious metals and stones. But it is Soper’s evening, as she shows us in every look and every gesture how her life with the man she loves has always come second to a royal fantasy.

Maurice’s Jubilee manages to convey both the pain and the stoicism of those facing certain death, without plumbing the depths of melancholy. The question is whether these disparate elements of fairy tale comedy, death, delusion and theatrical trickery can really work as a satisfying dramatic whole.