Prepare yourself: it's Harry versus Frodo round two

By 11am yesterday, two Glasgow primary schools had reserved seats for every pupil and teacher while a block booking for postal workers in Nottingham will take over an entire cinema.

Such behaviour, likely to be replicated in coming weeks in most households with a child aged five or more, could only have one possible explanation – Harry Potter and Frodo Baggins are back.

Advance bookings for the second chapter in the adventures of the wizard schoolboy opened yesterday, signalling the start of what has become the biggest annual battle for box-office takings – Christmas.

Harry Potter and the Chamber of Secrets will go head to head with The Two Towers, the second instalment of the equally popular The Lord of the Rings trilogy, in a repeat of the billing last year that eventually saw the films take £125m between them in Britain and £800m worldwide.

That haul helped the Christmas holiday season supplant the summer for the first time as the most lucrative period of the year for film studios, which have traditionally relied on the mixture of sunshine and long summer holidays to produce their most profitable hits.

Last year's offerings – Harry Potter and the Philosopher's Stone and The Fellowship of the Ring – were by some distance the biggest cinematic successes of 2001, despite making their money in dark months of winter.

Backed by two of the most sophisticated marketing operations ever seen, the fantastical tales of would-be magicians and hobbits both achieved placings in the top five highest grossing films of all time. The success has prompted Hollywood studio bosses to switch their attention to the winter period as the biggest cash cow of the cinema year.

Screen International magazine said: "With the two biggest hits of 2001 coming in the last six weeks of the year, winter has been declared the new summer."

Warner Bros, the studio behind the Harry Potter franchise, was clearly expecting to equal the £64m taken by Philosopher's Stone last year as cinema chains opened bookings for Chamber of Secrets, which is being released on 15 November.

A spokeswoman for Warner said: "The film last year had the highest advance box office sales. It broke all box office records, but this one is darker and funnier."

Odeon Cinemas, which is dedicating 228 screens to the blockbuster, said there had been brisk business for previews. Showcase Cinemas said it had received a flood of inquiries, including block bookings from schools in Glasgow and Teesside, and a booking of 1,000 seats from postal workers in Nottingham.

Advance bookings for The Two Towers, which opens in Britain on 18 December, are expected to start in the middle of October.