OMG I didn't want to mention I was too stubborn to change the gear too in case you thought I was really daft. I had gone up a smaller hill the day before on the middle cog (the gears on my left brake, the second one..I don't know what the proper name for it is sorry) and thought I could do the same on this hill..!! Anyway I've learnt my lesson, thanks so much for the great advice I'll remember to keep moving when I get off the bike and to use the right gears