Great, so am I right in thinking that the decision as whether to purchase as one transaction at £300k or two at £150k is somewhat trivial as the 'statutory formula used to apportion any expenditure' would likely split it at £150k each anyway as the houses are so similar?
But that formula only applies if it is a disposal for capital gains tax. Income tax takes priority over CGT. And it would not necessarily split it 50/50 because the formula considers the value of the part retained and the consideration for the part disposed of.
Yes, am aware that depending on our approach (selling, letting, living there) it will affect CGT/IT/PPR etc. Initially had the intention to rennovate and live there (one house each) but are now considering our options as we got it cheaper than expected at auction.
You haven't said how long you were intending to live there, but if it was going to be only a short period to try and secure PRR - and particularly if you then move back to your current home - HMRC would inevitably challenge it if they picked up the relevant return for enquiry.