He has been branded “the Banksy of punctuation” and describes himself as a “grammar vigilante”.

For more than a decade, an unknown corrector of poor English has been venturing out in the dead of night and tidying up the punctuation on Bristol’s shop fronts and street signs.

The identity of the man remains unknown but on Monday the BBC announced it had tracked him down and had accompanied him on one of his night-time missions.

He told the BBC he was a family man who worked in engineering. “I’m a grammar vigilante,” he said. “I do think it’s a cause worth pursuing.”

The man said he began by scratching out an extraneous apostrophe on a sign but had since become more sophisticated and has built an “apostrophiser” – a long-handled piece of kit that allows him to reach up to shop signs to add in, or cover up, offending punctuation marks. “This is a device that enables you to plant an apostrophe quite high up and get over any obstacles,” he said.

He also has a specially made stepladder that means he does not have to lean a conventional ladder against shop windows and carries a set square and scalpel to make sure his work is neat and precise.

The first sign he tackled, he said, was in 2003. “It was a council sign – Mondays to Fridays – and had these ridiculous apostrophes. I was able to scratch those off.”

Among the signs he has corrected in and around Bristol – the home town of the street artist Banksy – is a nail shop that used to bear the “gross” sign “Amys Nail’s”. “It was so loud and in your face. I just couldn’t abide it. It grates.”

He recently also took it upon himself to sort out “Cambridge Motor’s” – and was thanked by the owners when his handiwork was pointed out.

When it was put to him that what he was doing was probably illegal, his defence was staunch. “I’m sticking on a bit of sticky-back plastic. It’s more of a crime to have the apostrophes wrong.”

The Apostrophiser is on BBC Radio 4 at 8pm on Monday

