Before I travelled to Europe in 2016, I did some research to find the best SIM card for phone use in Europe. You can read about it here “3” SIM Card
If you are in the UK, you can get them almost anywhere for 1 Pound. If you are outside the UK you can get them from eBay or online from simcorner
After 12 months, my thoughts haven’t changed. If you have a Vodafone Australia account, for $5 a day extra you can use your Vodafone sim card, but after 2-3 weeks even that starts to get expensive. The “3” pay as you go SIM is still the best deal in my opinion. The “all you can eat” pack has changed a little, it as 25pounds this time, rather than 20, but still great value.
As the account doesn’t expire if you have a credit balance, I was able to use the same SIM card from last year, so as soon as I landed in the UK, I popped it in my phone and was online straight away.