Curry can certainly work well in a mass market. This is the UK, remember - even towns that can't manage to keep a shop, post office or pub going can boast an 'Indian' takeaway or restaurant. My little town of 15,000 can boast 2 restaurants and 3 takeaways - neighbouring villages have even more (including the legendary "The Gandhi, Sandy"). Every local shop and supermarket stocks entire shelves of microwaveable curries. The Tesco's up the road stocks frozen dosai and kulfi - and this is barely part of the country you'd call multicultural.

I think there's definitely something in what Swanhunter says. There are some 'brands' that are spreading through the country (Mumtaz, Café Naz, Tiffinbites, Masala Zone) but most of the chains that exist tend to be local operations where a successful, independent place manages to expand to a couple of neighbouring towns.