I have been sent a PAYE coding notice tax reference for April 2013-14 which mentions a place of work I have never been employed. How often does this mistake occur? I am on the waiting list for calling HM Revenue & Customs, but would like to hear any advice or common experiences with this problem.
That is very rare, unless and until somebody is fraudulently using your NI number. An employer generally updates HMRC about the employees it has taken up, their NI numbers for which it pays PAYE. Tax code notices come to you, presumably to close the loop and everybody in the chain i.e. you, employer and HMRC are on the same page. The best option is to intimate HMRC ASAP, lest you get into legal trouble.
The 2nd option is, has your employer changed it's name, or was taken over by a different company, in the past or currently, so the name reflecting in you tax code letter maybe different one, than what you know of.