GIft with Reservation of Benefit or POAT on shared house?

[Schizzlepops]

My elderly mother and I are considering selling both our houses and buying a single larger house together, where we would both live. Due to illness my mother is unlikely to survive 7 years so we will probably not save anything on inheritance tax this way, but it will help me to care for her. My question is how the sale of her current house will be treated for tax purposes (I own a share), and whether this will affect our planned purchase.

In 2008 my mother took out a mortgage on her house for £180k, and gave the cash to me to buy a flat, which I did. In 2010 i sold the flat and bought another. I sold that flat in late 2012, went into rented accomodation and used the proceeds to outright purchase a new house for my mother for £360k, while her old one was still on the market, to avoid her being stranded in a recently broken property chain. The new property was registered solely in her name, but a simple declaration of trust was drawn up stating that upon sale, 20% of the proceeds would go to me, and 80% to her. I rented the new property out for a few months while waiting for her old property to be sold (all rent proceeds came only to me). When it sold she gave me £180,000 cash, moved into the new property and has lived there ever since (not paying any rent on the 20% I own). I have never lived there.

Is the 20% share of her house that I beneficially own still going to be treated as a gift with reservation of benefit (eg by associated operations) even though I paid cash for the house, four and a half years and two flat purchases after she had given me £180k? Also from two property renovations I had over £180k of my own money by then, which I could arguably have used to buy my 20% share? Or will it come under POAT rules? If so, I believe it would be POAT exempt as 20% of therproperty's rental income would only have been £3000 per year, well below the £5000 chargeable threshold. i assume that either way I will have to pay CGT on my 20% share when we sell as the value is now £440k (I own my own home so this is a second property), but totally unsure how to account for it for IHT when the time comes, and unsure if it will affect us buying a new property together, which we would both live at.

[maths]

You received an absolute unconditional gift of 180k.

You bought properties and sold them generating cash of X. No tracing re reservation of benefit.

You then agreed with mother that as she couldn't sell her property in time to purchase a replacement residence you agreed to purchase the new property for her or, more precisely, you agreed to provide her with some funding to enable her to buy. You paid 360k. Under the apparent declaration of trust you retained a 20% interest. Mother therefore owed you 80% of 360k ie 288k. But she only paid you 180k (ie enough for a 50% interest). You therefore have made an outright gift (PET) of 30% worth 108k.

You don't live in the property.

I see no reservation of benefit or POA issues.