A British insurance firm is suing the producers of the US version of hit quiz show Who Wants to be a Millionaire - because it says the questions are too easy and it is worried about paying out too much money.

The US version follows the same format as the British original.

But while no contestant has ever won the jackpot in the UK, two lucky people in the US have answered all 15 questions correctly and walked off with the top prize, while three others have won $500,000 each.

The Goshawk Syndicate cites in its case questions such as: "Which of the following is a Latin dance: mustard, mayonnaise, relish or salsa [answer: salsa]."

Under its contract, Goshawk is required to pay out prize money to contestants who win $500,000 or more on the show - within a total prize money limit of $1.5m-$5m.

That means, for example, Goshawk would only be required to pay prizes to five winners of $1 million.

Unacceptable losses

In the lawsuit, filed at the High Court in London against Buena Vista Entertainment, Goshawk said it needed "significant changes in the level of control" to reduce the "unacceptable level of losses".

It asked for changes in the method of contestant selection and the degree of difficulty of the questions.

Observers say the show's broadcaster, ABC, is unlikely to alter the format of Who Wants to be a Millionaire.

The show has been a big hit in the US, attracting as many as 30m viewers a night, three nights a week, and has helped to establish ABC as the season's prime-time network leader for the first time in five years.

Other television networks have quickly tried to imitate Millionaire, to mixed success.

"The integrity of Millionaire is beyond reproach, and no one is claiming otherwise," ABC said in a statement.

"This is simply a dispute in which the company providing insurance is trying to deny coverage on the basis of a conversation it says it had with a broker."