As i understand it the law states:
Under section 8 pests act 1954 it is an offence, in respect of any animal, to use or permit the use of:
1. Unapproved spring traps.
2. Approved trap in unapproved circumstances.
The prohibition in section 8 does NOT apply to break back traps designed and used to catch small ground vermin (e.g. rats and mice) or the type commonly used for taking moles in their runs as these are made an exception under the Small Ground Vermin Trap Order 1958.
Rolfe.
You beat me to it Rolfe!
The STAO does not apply in this case, although the Duffus trap is