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The first preview of a West End musical version of Charlie and the Chocolate Factory has been delayed by five days because of technical problems.

Producers said there were "unforeseen problems in the delivery of a piece of stage engineering by a contractor".

The show, based on Roald Dahl's book, is being directed by Sam Mendes at the Theatre Royal Drury Lane in London.

The first preview performance was due to take place on Friday 17 May, but has now been put back to 22 May.

The show's website promises "ingenious stagecraft" to tell the story of the children who are led on a hair-raising tour of the fantastical factory.

But plans for a chocolate river - a central feature of the factory which, in the book, washes Augustus Gloop away - have already been abandoned, according to a recent story in .

The same article also said the set is so big that the weight hanging above the stage required the structure to have steel reinforcements.

The show is one of the most eagerly anticipated in the West End this year, and comes hot on the heels of the success of another Dahl adaptation, Matilda, which earned 12 Tony Award nominations for its recent transfer to Broadway.

Charlie and the Chocolate Factory is Mendes' first project since directing Skyfall, the most successful James Bond film yet, which has taken more than $1bn (£650m) at box offices around the world.

Willy Wonka is played by Tony-winning British actor Douglas Hodge.

In a statement, show spokesman Ryan Petersen said: "The whole production team is frustrated by this unforeseen delay in what has otherwise been a very smooth and exciting rehearsal period."