Thanks Petal, there are some interesting articles out there, personally I prefer unsmoked but it is the use of sodium nitrate which seems to be the element which causes the most trouble. Problem these days is that  only a very small number of companies control the market in the UK quite frankly the quality is dreadful and tantamount to consuming Gandhi's flip flop. 

DC You will be delighted to now I will not be calling on you for a bacon butty  Until a proper cure is found!