Who follows who?

I've owned CYB by default as a former NAB UK employee, but I've just bought some more in Aus when it dropped to $2. I have a bit of a beginners question when it comes to dual listed companies. I'm assuming the London price is the main driver for the Australian price, not the other way around, seeing as its business is entirely UK based. So for example, last night UK was up 5.8%, but today Oz was up just 4.27%. So you'd think UK would have to drop 1.5% today to match Aus price. But currently it is up another 4.5%. So being a UK business, does the UK share price just ignore what happens in Oz, and does that not open up some arbitrage possibilites if the two share prices don't follow each other lock-step?