For reds, I usually go for Cabernet Sauvignon from California (e.g. Gallo) or Australia but I especially like the Wanted Zin Zinfandel which I can get from Morrison's. It's often discounted, which helps. With whites, I've tended to stick to Chardonnays from Australia and South America but I've been adventurous recently and bought the odd Gavi and Pecorino from Italy and some French Sauvignon Blanc. I got a bargain bottle of Chablis earlier this year at £3.35 - I haven't tried it yet but for that price I can't complain too much if it turns out to be meh! I've yet to buy a bottle of Prosecco and I haven't bought Champagne in years. I find that a reasonably priced Cava is good enough for me; the Mark's and Spencer Prestige Cava - white or rose - are both excellent, particularly when they're sold for £8 a bottle rather than £10.00.