IMHO anaerobic activity is over rated. I've seen so many tanks with a deep layer of substrate that's been running for years with no anaerobic issues.....including my 3 year old 75gal set-up.the sand I got with the fish tank is very fine and I'm afraid of anaerobic bacteria forming if its too deep. plus finding a cheap (affordable) aquarium sand where I live its like trying to buy an elephant!
In regards to sand, don't you guys have pool filter sand in the UK? They are super cheap over here in the USA
+1.You shouldn't need too much. Just enough to cover the bottom and a little extra should be good. You don't have to have sand, but I think that having sand is better for the fish and makes the tank more pleasant to look at
Do what you want to do, whether it be bare or substrate, and don't let what's "popular" influence you.....its your tank