The first kit I did, I never really saw any signs of fermentation and thought my yeast was dud. However checking the gravity after a week showed me that it had happened i'd just missed it (must have happened overnight) You said in your post yesterday that you had bubbles in your airlock after 6hrs but the next day there were none. Mabey something has happened, like Orfy says I would check your gravity if you can.
Also are you using a fermenting bin/bucket which you bought in the UK. Some of the ones you get with the starter kits here are designed to be used without an airlock i.e the lid clips down all the way round but is not completley airtight and will alow the Co2 to escape.