“Love is a drug,” begins the opening number. No, it’s nothing whatever to do with Andrew Lloyd Webber’s latest blockbuster Love Never Dies, but it’s sung by three princesses, Mab, Dot, and Flora as they sit and sew, dreaming of love. Their father, the King, has gone off to war, leaving the key to his secret room with Flora, warning her never to enter.

Does she obey Daddy’s intstruction? Well, she tries, but in a strongly Cinderella moment, her two nasty sisters snatch the key, and are into the room in an instant. There they find a dusty tome, which reveals that Flora is destined to marry “The Pig from the North”. It’s not long before a heavy trotter is heard pounding loudly on the palace door . . .

Thus begins The Enchanted Pig, a Royal Opera House production aimed at young children. Originally staged in 2006, the show has more than a touch of Beauty and the Beast about it. Music is by the ever-tuneful Jonathan Dove, and the libretto comes from Alasdair Middleton. But the first thing that grabs you is the design — this is a world of amazing hair-dos and panto-style costumes reflected in revolving mirrors, with the lesser pigs first appearing in disguise as privet hedges. How, I asked director John Fulljames, did he come up with the design?

“We quite quickly decided that we wanted to stay in a fairy tale world, but ground it with reference points that would speak very directly to the young people that Dick Bird, the designer, and I knew. For example, his daughter was a big influence on the chav and goth costumes, which the princesses wear at the beginning — she’s an expert!

“Then there’s lots of head scratching. It’s about taking a notepad with you when you go away on holiday. You can be sitting on the beach, and you think ‘wouldn’t it be fun if the princesses had pointy hair instead of pointy hats’. There are so many different scenes and images in this show, in a way it was a bit like doing a crossword puzzle.”

Although The Enchanted Pig is primarily aimed at children, some of the show’s humour is directed at adults. For instance, there’s a scene very reminiscent of The Royle Family, ensconced on their sofa in front of the telly, and there’s a northern lady with a book on top of her head — John Fulljames didn’t quite give me a straight answer when I suggested that she might be a female version of Alan Bennett.

“I suppose there is something very dour about her!” he laughed. “The joy of the piece is that it does work on so many different levels. You can respond to the grotesqueness of rolling in the mud, or kissing a pig, or the wee and fart jokes. On the other hand, it can be a piece about growing up, or having your first boyfriend. Or it can be a Freudian deconstruction of sex. You can take it on any level.”

Whatever the level, it’s vital that the words come over clearly over the top of the six-piece band, who play Jonathan Dove’s score: just as the words are vital in Stephen Sondheim’s shows.

“Sondheim is a very good model,” John agreed. “The show expands into something more operatic than Sondheim, but the number [here he launched into song] ‘Don’t fall foul of fairies, don’t go kissing frogs’ really smells of his Into the Woods.”

Unlike politicians, opera people don’t have to pretend they never make mistakes. Have there been changes in the four years since The Enchanted Pig was first produced?

“We’ve changed it quite a bit,” John told me. “It’s fascinating going on a journey a second time, with the benefit of hindsight. Last time we did 80 performances, which for a new opera is almost unheard of. So we know how audiences react — that’s a hell of a lot of feedback we’ve had. So, for example, we’ve redesigned Act Five, the point when we reach the palace of the Wicked Witch, to make the storytelling clearer. Also, we’ve trimmed the length a little bit.

“The first time we did the show, we were terrified whether it would hold the kids, or whether there would be a riot in the audience. It was a joy when not only the six plus children — the minimum suitable age we advertised — but also their four-year-old brothers and sisters were rapt by it as well.”

The Enchanted Pig is at the Oxford Playhouse from Thursday, April 15, to Sunday April 18. Tickets can be bought on 01865 305305 or online at oxfordplayhouse.com