Allowable absence, letting and CGT

Someone has just phoned to ask me capital gains tax advice on a property that used to be her PPR until she and her husband (although they weren't married at the time) moved to Australia. They have now returned to the UK and are living in the property. She phoned HMRC twice and was told both times that she would have no CGT to pay when she sells the house as she was working in Australia and it was thus an allowable absence.

My view is that allowable absence only counts if you leave the UK in order to work overseas by prior arrangement, not if you emigrate and then find a new job out there. But maybe I'm wrong - does anyone else know for sure?

As far as CGT goes, I don't think it makes any difference in her case, because even if it was an allowable absence, the fact that she let the property out the whole time she was away would make it taxable for this period anyway, even if it was still her PPR. After all, if she had let out part of the house whilst still living there, that would create a CGT liability on the percentage let out, unless (I believe) it was covered by the rent-a-room exemption (although I may be wrong about this).

It worries me that HMRC give out that sort of advice without knowing the full facts, which then flies in the face of what I told her.

Useful comments on this would be appreciated.

Chris