I don't have a high level of interest in this issue, but there was an article in the Telegraph today that calculated the tax might cost a woman 75p per year.
Discussions about VAT invariably annoy me, as they end up with people say X is not a luxury. VAT is not a tax on luxuries, in theory it should be charged on everything, though for political reasons a few things are exempted or have lower rates. Given the country has a social security system which is capable of taking the tax on "necessities" into account in computing what it expects people to live on, I think we should simplify and just charge VAT at the same rate on everything.
If you want to ease the burden on people who struggle to afford tampons, electricity and gas, fresh food, or children's clothes, compensate them via the benefit system, which is geared up to looking at each persons circumstances, rather than having across-the-board reductions everyone benefits from, and court cases deciding whether something is a biscuit or a cake.