Green’s Dictionary of Slang

lagging n.

[lag v.2 ]

1. [early–mid-19C] (UK Und.) a sentence of transportation; thus lagging matter, any crime punishable by transportation.

2. [mid-19C+] (Aus./UK Und.) any prison sentence.

3. [mid-19C+] a sentence of more than three years’ imprisonment.

In compounds

lagging dues (n.)

1. [early–mid-19C] transportation; e.g. lagging dues will be concerned, this person is liable to be transported.

2. [late 19C] a sentence of penal servitude.

lagging station (n.)

[20C+] (UK prison) a prison for long-term prisoners.