I'm not sure that anyone has suggested that you are. Just bear in mind that a small claim is your only real redress, and that it will likely only be a moral victory. There is also a risk that if it goes to court and the judge decides that your claim is frivolous that you could be ordered to compensate the farmer for attending (£90). So worst case is it will have cost you £140 or thereabouts.
Best case is that you will have an outlay of £25 which you may get back with your £10-£15 that you are presumably claiming, and that the farmer just pays you off. Most likely case is that you will have to spend some time going to court, outlay a further £25.
It seems like an awful lot of hassle for a puncture, and there is a degree of risk that you will lose and be further out of pocket.