Vermiculite holds water, perlite is better for drainage & helping with temperature changes in pots. But horticultural grit may be best of all for drainage alone

Thanks Darren. It's good to know the difference.

Hi, when I was an apprentice gardener, [many moons ago] we used vermiculite for rooting cuttings, as it stayed moist longer than compost, perlite allows more air around plant roots aiding drainage, vermiculite is expanded mica, while perlite is a volcanic glass, Derek.

Wow Derek, so many knowledgeable gardeners on GOY and we all benefit.
Darren, I went shopping today and had to get perlite because the shop didn't have any manageable bags of grit. We non-drivers have to explore ways to obtain bulky items at not too much extra cost. Ebay and Amazon are ok but quite dear. My milkman delivers compost and soil improver with free delivery. Garden centres charge for delivery and it's worth it when one orders a few large items. I can really understand why most people feel they cannot live without a car but it's certainly possible in a city like Exeter.