Agree with all of the above and add that a simple call to your shooting organisation will confirm or otherwise the validity of the advice obtained from this or any other forum.
I put a scenario to BASC and they supported my contention that I could validly shoot out of season to prevent damage.
It might be described as a "farmer's defence" but the CPS would, I suggest, not embark on a prosecution in the full knowledge that the S7 defence would be offered at any proceedings. The RSPCA on the other hand, may just do that, if there was mileage in it for them. But they have bigger fish to fry, although they can and do undertake private prosecutions at little risk to their finances.
S7 Deer Act 1991:
7
Exceptions for occupiers etc. of land where deer are.E+W
(1)Subject to subsection (3) below, a person to whom this section applies shall not be guilty of an offence under section 2 above by reason of—
(a)the taking or killing of any deer by means of shooting, or
(b)the injuring of any deer by means of shooting in an attempt to take or kill it,
on any cultivated land, pasture or enclosed woodland.
(2)Subject to subsection (3) below, a person to whom this section applies shall not be guilty of an offence under section 4(2)(a) above by reason of the use, for the purpose of taking or killing any deer on any land, of any smooth-bore gun of not less gauge than 12 bore which is loaded with—
(a)a cartridge containing a single non-spherical projectile weighing not less than 22.68 grammes (350 grains); or
(b)a cartridge purporting to contain shot each of which is .203 inches (5.16 millimetres) in diameter (that is to say, size AAA).
(3)A person to whom this section applies shall not be entitled to rely on the defence provided by subsection (1) or subsection (2) above as respects anything done in relation to any deer on any land unless he shows that—
(a)he had reasonable grounds for believing that deer of the same species were causing, or had caused, damage to crops, vegetables, fruit, growing timber or any other form of property on the land;
(b)it was likely that further damage would be so caused and any such damage was likely to be serious; and
(c)his action was necessary for the purpose of preventing any such damage.
(4)The persons to whom this section applies are—
(a)the occupier of the land on which the action is taken;
(b)any member of the occupier’s household normally resident on the occupier’s land, acting with the written authority of the occupier;
(c)any person in the ordinary service of the occupier on the occupier’s land, acting with the written authority of the occupier; and
(d)any person having the right to take or kill deer on the land on which the action is taken or any person acting with the written authority of a person having that right.