To most viewers, Channel 4 quiz show Countdown is a relatively safe programme to watch with sensitive souls. With only two contestants, a few numbers and a couple of letters - what could go wrong? It turns out quite a lot as co-host Rachel Riley found out on Monday.

Rachel RileyCountdown host Rachel Riley was left red faced after she spelt out a choice word on the show

The Maths wizard was putting up randomly picked letters on to the board as usual but realised something was going terribly wrong as she spelt out the word S-L-U-T.

This was followed by nervous laughter from the contestants and fits of giggles from the audience which was further increased when the next letter was Z - spelling out S-L-U-T-Z.

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While Rachel simply wanted to "speed things along", Countdown main host Nick Hewer found the funny side of the incident with a wry smile.

Fortunately for the contestants, the saucy letters did not put them off with the winning word coming out at seven letters: SALUTES.

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Clearly unable to shake her uneasy feeling, Riley tweeted after the show: "Never work with kids, animals or letter tiles! #occupationalhazard".

This was the first show back for the former Strictly Come Dancing star after a holiday in Bali but it is not the first time a rude word has appeared on this mild mannered show with Myleene Klass spelling out gobsh**e during her stint on the show earlier this year.