Possibly somebody wiser than me can correct here but on the face of it, what is proposed is illegal ?

from the BASC website.

Under 14 years
You can
• use an air rifle under supervision on private premises
with permission from the occupier - normally the owner or tenant. The person who supervises you must be at least 21 years old.

You cannot
• buy, hire or receive an air rifle or its ammunition as a gift, or shoot, without adult supervision.

Parents or guardians who buy an air rifle for use by someone under 14 must exercise control over it at all times, even in the home or garden.
It is illegal to sell an air rifle or ammunition to a person under 18 years of age.


Bit confusing ?