Cheers for that, but it only part answered my question. 

So assuming this is then legal and a suitable arrangement for tax purposes……

There will be no capacity issues servicing the debt at my end. Properties are so positively geared its ridiculous.

The properties are security. No chance of Mum losing her money whatsoever. Both our wills are up to date as well.

I think it's just a matter of Mum and I nutting out the details of the loan so we are both happy and protected. I think Mum is looking at a similar arrangement with my sister so can't see any elder abuse issues. I'm paying her more interest than the bank in a term deposit.