The success of University Challenge proves that TV does not need to dumb down, host Jeremy Paxman said.

The presenter, who also hosts Newsnight, said the questions had deliberately been made tougher. Paxman was asked by the Radio Times whether the standard of questions was lower than at any point in its 40 years on air.

"For heaven's sake, do you watch the show?" he responded. "We have intentionally made the questions harder. And they get harder still as the series progresses."

He continued: "It might be interesting to speculate on why it is that a quiz in which much of the audience doesn't expect to get most of the answers right achieves such spectacular ratings, in a difficult slot."

He added: "I think it proves that television doesn't have to dumb down. If you pay the audience the courtesy of inviting them in by suggesting they're quite smart enough to go along with the programme, they will come in."

More than 4,000 questions are commissioned every series, of which around 3,250 will make it to the screen.

Paxman said he only "very occasionally" rejects a question, "on the grounds that I didn't understand it, or couldn't pronounce it", and he only rewrites "a small proportion, mainly to make them easier to read aloud at speed, or removing the occasional split infinitive or dangling modifier that has slipped through in my role as in-house grammatical pedant".

Peter Gwyn, University Challenge executive producer for the past 14 years told the magazine he was "in no doubt whatsoever" that the questions are tougher than in original quizmaster Bamber Gascoigne's day.

"We ask far more on the sciences than we ever used to, for example, and in far more detail," he said.

But he said more clues are also given nowadays.

"In the early years of the show, a question would require a piece of general knowledge that you either knew or you didn't.

"These days, we give more clues - perhaps the century, perhaps the country of origin. Sometimes we give as many as five clues in a question, in descending order of difficulty, ie hardest first."

Paxman was quoted last month telling the The Times Cheltenham Festival of Literature that University Challenge had been "dumbed up" since the show's early days.

But Gascoigne, who started hosting University Challenge in the 1960s, was previously reported by the Evening Standard as saying: "The few times I've seen it he's (Paxman) much more beastly to the contestants than I was."