Keith A of Hertford wrote: It is a holiday advert that I am getting because of recent searches.
So I take it that it's always the sane advert. If so it could be clickjacked. See Malvertising
I also asked what browser. Some are more susceptible. If it's Internet Explorer, what version?
If you draw the cursor down over this sort of Google ad the cursor normally changes shape. You may find the click area extends below (or beside) the advert and covers several links. Sometimes this is just an error rather than malicious. Happens often on one forum I use.