Depending on how big your constituency is, the numbers probably look better in actual signatures rather than in percentage terms.
If you are writing a letter, bearing in mind the initial response may just be quoting DEFRA, my advice would be to check DEFRA’s initial response to the petition and counter the things they mention. i.e. Tunnel – optional extra – additional payment required. Trap still sold unaltered from original used to kill hogs in NZ. Tunnel not fit for purpose – Hogs could get stuck in it and die slow death – a selling point of trap is that no need for frequent checking. Humaneness – a dead hog is one dead hog too many whether killed ‘humanely’ or not. We know it is against the law to trap and kill hedgehogs, but how could they possibly enforce this, etc. Good Luck.
Hope your son is being successful getting more support.