I first heard about this on NBC Nightly News back in the '70s. The British were
actually developing an anthrax bomb. What if they did?
Another form of deterent? Honestly, as long as the USSR has nukes pointing at you, the British will never seriously consider using it. Then the news leaks out, and you have thousands of people in the streets protesting biological weapons while the superpowers engage in a biological warfare race. Assuming minimal butterflies, the fate of soviet germ warfare scientists after the collapse of the warsaw pact in relation to terrorists is a worrying prospect. Finally, I can easily see a labour government scrapping the bomb for various reasons (mostly moral).
Net result: Somewhere between a visibly identical world to one ravaged by manmade epidemics.