Thank you for your posts. In answer to your question: there's no good reason for the house now (apparently) being worth £300k more than when it was valued 1.5 years ago. I put the discrepency down to (a) some imporvement in the housing market and (b) the estate agent being more 'bullish' than the surveyor. Of course we may not achieve £1.5m - it is just the estate agent's recommended marketing price.
I guess I could rephrase my question slightly to make it more hyperthetical: when selling an inherited house, at what point does CGT become applicable rather than IHT? Taking my situation we could envisage two scenarios at opposite ends of the timeline spectrum:
Scenario 1: A few months after my father's death we sell the house for £300k more than the valuation used for probate. In this scenario I am failry certain HMRC would require us to re-calculate IHT based on the true/realised value of the house.
Scenario 2: We decide to live in the house rather than sell it. 20 years in the future we sell the house for £300k more than it's probate value. I am fairly certain HMRC would expect us to pay CGT on the £300k capital appreciation (or nothing if it is our primary residence). I assume they would not expect us to revisit the IHT calculation 20 years down the line.
So at what point do we switch from having an IHT obligation to a CGT obligation? Is it down to length of time between grant of probate and the sale of the house? If so is there a specified amount of time? Apologies if I'm missing the point here... I'm quite new to this!