The measure was intended much more to force this result than it was to generate revenue. It generates little, and its forecast was revised down several times.This demonstrates the "unintended consequences" of the sugar-tax rather well: rather than put up prices, manufacturers have changed their formulae to reduce the sugar content. In terms of preventing obesity that's a result, but does mean that the revenue from the "sugar levy" won't be as high as forecast.
I think that now the correct thing to do is eliminate the exemptions for fruit juices and milk-based drinks, then start lowering the upper threshold.
It was also notable how some manufacturers and retailers took the opportunity to simply increase the price of all drinks to take account of the new levy.