Just to chime in, I find food in the UK VERY cheap, and I'm basing this on London standards. It is the one thing that REALLY surprised me about London when I moved here. I work in Oxford Circus which is as central as you get, and I spend <£10 for lunch (<£100hkd) and that can get me anything from Vietnese Pho with a spring roll and coffee, pulled pork sandwhiches with chips and slaw and a drink, roast duck beijing/hk style with rice and veggies, etc. There are many ~£5-£6 options, as well.
If I go to the market, food just generally is f'all cheap. When I have been on extended business in HK, I did not find supermarkets terribly cheap at all and found it was usually cheaper to actually eat out at hawker stalls (<$40-$50 for duck and rice). Wetmarkets will yield better deals. That said, you have to be mindful of food quality in HK, too, as much comes from the mainland and is rather questionable.
All said, you can probably have a food budget that would mirror London if you tried (though again, you wouldn't have the diversity in HK for that same budget that you would for London). I suspect CH food prices, though, are higher than London and more inline with what I had when I lived in Holland (Holla
nd was more than London or HK). So you may be alright. The best way to compare is to see what you enjoy eating, how much you pay, and what you'd have to pay when you move (with a bit of flexibility for localisation, but not completely local b/c you probably, assumedly, you aren't Canto).