The Knock is a British television crime drama, created by Anita Bronson and broadcast on ITV, which portrayed the activities of customs officers from the London City & South Collection Investigation Unit of HM Customs and Excise.

The only three cast members to appear in every series were Caroline Lee-Johnson, Trevor Byfield and Steve Toussaint.

The fourth series consists of six episodes, and was broadcast from 7 January to 11 February 1999.

This series was the last to feature many of the original cast members, including Enzo Squillino, Jr. and Andrew Dunn; and was also the last series to feature multi-part stories (in this case, two stories of three episodes each).

The fifth and final series consists of four episodes, and was broadcast from 21 October to 11 November 2000.

The format of the series was also very different, featuring four stand-alone stories, with the running time extended to 105 minutes per episode, with advertisements.