The bar top might be gleaming, and the kitchen may be spotless - but there’s a stomach churning secret in thousands of pubs that it’s impossible to spot.

Beer lines – which transport your tipple from the cellar to the glass – are often neglected, meaning beer, lager and cider flow through dirty pipes before they’re served.

And the drink that’s most at risk of coming through neglected pipes is the classic summer drink: cider.

What’s more, the area most likely to be serving cider from dodgy pipes is the area best-known for the drink – the south west.

The conclusions were compiled by pub inspectors from Cask Marque, who aggregated data collected in part from 220,000 smart devices attached to beer taps.

They found that 44% of ciders were pulled through unclean pipes, a higher percentage than any other drink.

Stout followed on 36%, followed by lager (35%), keg ale (31%) and cask ale (29%).

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There are big variations by region, too. The north east had the best-kept lines, with only 29% of drinks being pulled through unclean lines.

That’s more than 10% lower than in the south west (40.8%), the worst-performing region.

Close to half (48%) of pints of cider in the south west came through dirty lines, the report found.

Cask Marque – an independent accreditation scheme for beer quality control – said pubs may be skipping cleaning duties to save money and beer wastage.

Director Paul Nunny told The Morning Advertiser: “Consumers today expect good retail standards and this has added to the demands on the pub.

“We have now got a lot of fast food outlets that are competing with pubs and so are coffee shops, only their standards are higher and pubs need to catch up.