I agree with Starbug, the market is there. The Mexican place mentioned sells cooked food as well as packaged and dried Mexican foodstuffs at prices that are extremely high, even by Swiss standards, yet they still do a booming business. Although I'm an American, I've spent a fair amount of time in the UK and certainly have foods from the isles that I like. Many UK foods are available here in the high-end grocery stores like Loeb and Globus but a presence on the Waisenhausplatz a couple of times a week (and then online sales also) would definitely be a business I would patronize.
You can try the Bern Chamber of Commerce for info:
http://www.bern-cci.ch/de/
German and French only.