As long as the relative proportions remain the same, the difference in measure sizes isn't really significant. The problem only arises if you try to convert from cups to mililitres or grammes.
The slightly larger UK cup size just means you end up with slightly more finished product. Just remember to use the same measure for all the ingredients.
If you're really picky, you could add a little extra salt and sugar, but I've used this recipe and it works OK.
Alan
They're not absolutely critical anyway. The measures should be your starting point. Then you adjust for taste (some like it thicker while others like it thinner)