If you had an terminal block or lighting block, in,or on the celing. There would have been 4 connections,
permanent live, usally two, or three red cables,
a neutral, usally one,two, or three black cables,
earth, Yellow and green,
and the switched live, (see below).
The switched live is usually a black with red sleeving or red insulation tape around it, or it may be another red cable. This connects to the brown cable of the old light.
The switched live all depends on how it was originally wired.
I the older days, or dependant on who wired it, the switched live cables were left as black, which is very confusing for the DIYer. Who would have thought that this was a neutral.
I bet what your hubby has done is to connect the permanent live to the light (brown cable) and not the switched live.