The catchy theme tune, "Eye Level", reached number one on the U.K. charts at the end of 1972 when this show was first shown and stayed on the chart for twenty-four weeks.
The theme tune, "Eye Level", has the distinction of being the first television theme song to top the official U K. chart.
Although exterior location filming took place in Amsterdam, all interior scenes were recorded at Thames television studios at Teddington Lock, Middx.
When this series first debuted on the ITV network in 1972 it touched on surprisingly adult themes such as pornography, homosexuality, hard drugs and child murder, quite groundbreaking stuff for a UK made TV show at the time. This inevitably meant it had to be shown in the post watershed (9pm) time slot.
Barry Foster, Geoffrey Bayldon, and David McKail are amongst the very few actors to have acted in the 1970s seasons and the 1990s seasons.