I don't think it's necessary to buy British just try to avoid, or minimise, the purchase of goods where you would deem workers to not be getting a fair shake of the stick. A level of competition is healthy but we can't introduce minimum wage, health and safety, etc, etc and then just export our poor practices to other countries.
For example, I'm happy to buy from Germany - Rohloff, Supernova, Schwalbe, Schmidt as I didn't see a viable UK alternative - I also chose Ortlieb over Carradice based on function and form - but I do buy Hope stuff, hubs, stems, headsets, spacers, seatpost clamps
There is no reason that the UK can't compete in more areas but it does require the right sort of investment. It's no good relying on individual entrepeneurs and those with a passion and money. We need to make manufacturing investment more attractive, especially in relation to financial/property speculation. There are a myriad of ways to do this and we can learn from Germany in this. One key thing they do have is far less of a 'them and us' approach coupled to stronger workers protections.