I have also posted choccy bars abroad (USA) - it's not cheap to send them airmail (which takes about 7-10 days) so a cheaper option is to go for surface mail but this may take 6 or so weeks. As evedawn says, you will need to fill in a Customs Declaration Form (CN22) - more info here http://www.royalmail.com/portal/rm/content1?ca tId=400044&mediaId=400362
Two years ago, I sent Easter eggs to my daughter in Australia, and they were returned to me several weeks later, having been opened by customs (perhaps they could smell the choc!). So, I agree with the earlier answer, that Aussies are paranoid about letting food enter their country (or perhaps they don't want other Aussiers to know that English chocolate is better than theirs)
Thanks for your replies. I took a chance and sent them. They arrived the other day, in one piece!! On the parcel certificate i just wrote easter gifts. Perhaps i wont be so lucky next time!