Some Co-ops have Keens mature unpasteurised Cheddar in their Slow Food range (the cathedral City should be avoided if you want real cheese) and all Globus stores should have Montgomery's cheddar (prob the best in the world) but they are both pretty pricey. I'm not sure yet what Migros cheddar is or where it comes from.

If you want a very good mature cheddar at a very good price, PM me