A recently-launched local newspaper has already been forced to apologise to readers after it published an obscenity ‘inappropriate for a family newspaper’ hidden within an advert.

The Dyfed Powys Police have reportedly been alerted, after an apparent sabotage effort in which a list of services offered by Enterprise Rent-a-car was doctored to include “c**k sucking”.

The embarrassing error appeared in just the third edition of the Pembrokeshire Herald, which was launched in west Wales on 5 July.

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And it went unnoticed until after a run of 20,000 copies had gone to print, which remained on sale despite the mistake.

The journalism news site Holdthefrontpage.co.uk reported that newspaper bosses at the Herald had written to police about the advert, saying they believed it had been altered by an unauthorised person.

Changes were apparently made throughout the paper, though only the Enterprise ad contained an obscenity.

The website reported publisher Tom Sinclair saying: “A number of adverts in last Friday’s newspaper had additional copy inserted into them after they had been proofed and signed off.

“The extra copy contained language that was inappropriate for a family newspaper like ours.

“I would like to make it absolutely clear that the adverts were altered without the knowledge of our advertisers or this newspaper.

“The pages had been signed off and were ready to go to print. I would like to apologise to our readers and advertisers for any distress caused.”

The blunder started to receive attention on Twitter when readers posted pictures of the offending page, and it was spotted by TV and radio presenter Jeremy Vine who asked if it was “for real?”.

Other users speculated that it might have been the work of a "disgruntled employee", while social news website BuzzFeed UK (@BuzzFeedUK) called it simply an "astonishing advertising fail".