Well it happened again tonight and since it's only been a week i phoned up Orange and asked them to send me a new one.
Will get a replacement tomorrow, my advice to anyone with an issue (well maybe just in UK) would be phone up your service provider and if it's within warranty ask for a new one and don't let the fob you off by sending you to the Apple store.
I hink it helps if you phone up more than once, as well, so phone one day do what they say to do, then phone up the next day and say it has happened again (which in my case it really had)
I'll keep you posted if the next one does the same thing.
On a side note and maybe/maybe not related but i wasn't receiving any emails (me.com from migrated to icloud) regularly either and had to sync manually to get them, where as my wifes would come through normally as they did on my 3gs