is down to the bland tastes of your average British punter
No it's not. It's because most non-chain restaurants are crap, and you don't want to ruin your evening going there and waiting hours for rubbish food, so you pick something that you know – this is usually a chain. Yes, you get crap service at some of those too, but they tend to be less crap overall than a crap local.
I've often been to oh so simply lovely bloody picturesue family run traditional olde bloody italian bistro restaursnts that turn out to be less tasty than a chain and much less tasty than a jar of Lloyd Grossman.
FWIW the worst Italian food I ever had was at a restaurant in Rome. I ordered carbonara, which I know is boring but I really fancied it, and it came out scrambled egg. How they had the gall to serve it when they knew they'd cocked it up is beyond me.
And the reviews on Google are useless. If someone says it's good, you've got no idea what their standards or tastes are. Places I know for a fact are dreadful get great write-ups.