Agreed, but on a more general note, you should at least make sure that you have a few UK credit cards to hand when you come over here (with 0% cash transfer facilities). They were invaluable in our first few months when cash flow was tight as we came with nothing like you.
Note - I am saying I used them to help with cash flow not a house deposit!!!
That said, they could have been used for that.

Looking into a morgage offer, Kiwibank has just turned us down as they class our residency visa as 'temporary' - just interested from those who have managed to get a mortgage who you dealt with?

We managed to get our mortgage while we were on WTR visas. We went with ASB. We already had a bank account with them before approaching for a mortgage and to be fair we had a bit more than the 5% deposit. The visa simply wasnt an issue and we have found ASB to be incredibly helpful over the years with everything from our mortgage to money transfer and insurance. Now if we pay the damn thing off life would be much easier! Another stint in the Middle East is needed

both times we bought we got a mortgage within 6 weeks of being in the country with Westpak, kiwi bank also turned us down even though we had PR