They certainly used No4's F10, I would imagine both mk1 and mk2's
The RUC used them and they were avalable for use by mainland police forces too, I don't know how many used them though?
Back in the 1970's a local farmer to me had to call out a Police Marksmen with a No4 to "despatch" a totally crazy breeding bull that went on the rampage... Big game hunting in the Cotswolds!