SOME of my longest moments have been spent sitting in pantomimes. “Oh no they haven’t,” says Howard Panter, quick as a flash.

Oh yes they have. Panter, boss of the Ambassador Theatre Group (ATG) and a prolific backer of pantos, creases up in giggles. His company may be the biggest owner of theatres in London’s West End, and the second-biggest owner of regional venues, and a very serious theatrical producer but, boy, does he love to laugh.

One minute he’s explaining ATG’s expansion plans, the next he is flicking in jokes, happily debunking the pomposity of luvvieland. And at times he just marches his own conversation smartly over a cliff.

“We are looking at two buildings that could fill gaps in the market,” he says, describing his schemes for new theatrical spaces in London. “One is an established theatre, the other is a found space — actually, that’s a terrible phrase, why am I saying ‘found space’? Do you get ‘lost space’? I don’t know. It’s so pretentious. Did we just stumble across it? Or...”

He looks bewildered and stops, scratching his cropped head. “Sorry, what was your question?” Then he grins. With his well-fed tummy, fruity delivery — Sir Donald Sinden out of Hillingdon — and winning befuddlement, Panter wouldn’t be out of place on any panto stage.

Yet he and his wife Rosemary Squire have built ATG into one of Britain’s leading theatre and production businesses, now expanding fast and packing a cultural punch way above its profit of almost £4m on sales of £62m.

Last Thursday ATG opened its £3.5m co-production of Porgy and Bess, on which a lot of next year’s success could hang. When we meet, in a poster-lined room above ATG’s Duke of York’s Theatre in St Martin’s Lane, the first reviews had yet to appear and 57-year-old Panter is fizzing with anxiety over how critics and audiences will take to the production.

“Porgy and Bess is a ravishing performance and a thrilling production,” he enthuses, “wonderful songs — Summertime, It Ain’t Necessarily So — a passionate, sexy, tragic love story...”

But Panter also knows that the production, which turns George and Ira Gershwin’s opera into a musical, could easily fall between two stools: too highbrow for Friday-night revellers, too lowbrow for buffs. Advance ticket sales have been moderate and the competition — Spamalot, Wicked, Dirty Dancing, ATG’s own Guys and Dolls — is fierce.

Who would be a producer? Panter, of course. “I’ve loved the theatre from my earliest days,” he gushes, “since my parents took me to a pantomime, and I saw the golds and the reds and the warmth and the feeling of magic.”

Panter, the son of an engineer, had worked his way up through every backstage job, before a fortuitous meeting with the property tycoons Sir John and Peter Beckwith pushed his theatre management to another level.

Now ATG is one of the biggest and broadest operations in theatreland: buying theatres, producing plays, running a ticketing arm, expanding into television production — it recently co-produced Channel 4’s The Play’s The Thing.

All of that brings it into competition with Andrew Lloyd Webber’s Really Useful Group, and Cameron Mackintosh’s theatre and production business. Next it wants to snap up theatres in New York and Europe, and push its productions round an international circuit. Panter and Squire hope to float the business before 2010, giving their backers the opportunity to get their money out.