“EeEh, Joseph, am I glad to see ya. Our Jesus has been a little bugger all day.” Welcome to the school nativity play, a performance nominally set in Judea 2,000 years ago but actually located at the heart of modern British culture. Some six in seven primary schools stage them. But why, in this secular age, do they remain so popular?

It’s partly because even though they’re specifically Christian they aren’t remotely exclusive. Pupils of all faiths and none can join in (pages 22-26). Parents instinctively accept that creed, or lack of it, isn’t as important as the opportunity to applaud their children on a public stage and assail friends and relatives with pictures of their phenomenal talent. Parental pride trumps dogma every time.

Nativity plays are also endlessly elastic. In recent years, the cast of characters has expanded enormously. Sheep, palm trees and camels have been joined by horses, rabbits and cacti. Phalanxes of angels are so yesterday. Adventurous impresarios have added lobsters, bats and cowboys. One school in Kent even scripted a Liz, Mary’s hard-drinking cousin, and had an adult Jesus turn water into lager.

There has been some pushback from the Church. The Pope wrote recently that animals probably didn’t feature prominently at the gig in Bethlehem. Is he mad? How reckless can you get? Taking a stand against gay marriage and the ordination of women is one thing. But trying to write Donkey Daniel out of the script is playing with fire. Clearly, they don’t properly appreciate the importance of school nativity plays in Germany.

It’s true that some of the original parts have taken on far greater prominence than Matthew and Luke intended. The innkeeper has become pivotal. Hearty hosts regularly invite Mary and Joseph in for a drink, ruining the entire plot. Belligerent hoteliers can be just as damaging. “Folks like you who leave it to the last minute make me sick! Now sod off,” screamed one at a Joseph who had neglected to go online and book a room in advance.

Unscripted subversion is key to the play’s enduring popularity. For every weary Mary, there will be an off-message innkeeper, a tongue-tied king and several unconvincing sheep. There is scripture and there is ad-libbing, nose-picking and arse-scratching. It is holy and hilarious, magical and absurd. You only had to look at the orchestrated pandemonium of Danny Boyle’s Olympic ceremony to see that there must once have been a teacher who years ago ushered him on to a stage wearing a cardboard halo and made him believe he was playing a part in something wonderful.

So, to all those teachers who over the years have volunteered hours of their time to sustain a great national institution, thank you. The buckets of glue, acres of tea towels and silos of glitter were not pressed into service in vain. Who knows how many of the country’s finest talents were ignited by encountering for the first time exotic angel wings, mysterious myrrh or that sublime classic A Wayne in a Manger? But to those unknown teachers who years ago cast David Cameron as the Archangel Gabriel and George Osborne as Herod, well, are we feeling so clever now?

Merry Christmas.gerard.kelly@tes.co.uk.