I was just parroting what an examiner had told me the day before. And also every FI I ever met
As you found, and I dare say predictably so having been through the PPL training scene myself 10 years ago, they were feeding you bull
You need to carry suitable data for the flight, basically. It doesn't even have to be in paper form - 100% electronic is legal (if not necessarily wise - another debate).
There are some countries, I vaguely recall, which do require the carriage of a
printed chart, but it's nobody anywhere near here.
On a different tack, the UK CAA (and I think almost every other CAA in Europe) has a monopoly on the publication and sale (and profit generation therefrom) of VFR charts. It would then be rather rich of them to require the purchase and carriage of these... probably illegal under EU competition law.
On a different tack again, there is VFR and there is IFR, and anybody wanting to get into mandatory chart carriage under IFR is going to get into a right pickle. And that's before one gets into the UK Class G scene where you can switch VFR-IFR non-radio, etc.