This was the team's third single on the EMI label, their sixth overall, and the song that finally brought Chas & Dave to the attention of the British public. Backed by "The Banging In Your Head," it was the first of their releases to make the Top 50, peaking at #20.
As might be deduced from its title, this is a novelty song, "Gertcha!" a popular East End exclamation of disbelief - and sometimes a mild threat - being what the singer(s) old man would utter when riled. Old man in East End parlance referring to one's father.
Unsurprisingly, "Gertcha" was used in a TV commercial for beer.
Suggestion credit: Alexander Baron - London, England, for above 3