We got back to the UK at Xmas, and are in exactly the same position: large deposit, but not large enough for a cash purchase. And yes, it's a problem.
Banks in the UK are very fussy lenders these days, and having a large deposit isn't enough to convince them you're worthy of a mortgage. Whatever employment history you can provide from Australia isn't relevant; whatever you earnt in Australia isn't relevant; whatever UK credit history you had before you left isn't relevant (ours was fine, and we were only away 2 years) and nor is your Australian credit history. What they want is a history of UK residence and employment, demonstrated by your P60s. Basically you tick none of the boxes.
We went to a specialist broker who tried various weird and wonderful lending institutions. He got most interest from the international credit banks, who are like less likely to be phased by getting overseas tax returns, credit references, etc. But he still got no offers for us, and even if he had, the rates they wanted were off the scale.
We've given up and resigned ourselves to renting for a couple of years.