Readers’ forum: Selling family home at undervalue

My client inherited a half share of his mother’s house when she died some years ago. He agreed with his sister that she could continue to live in it as long as she wanted; she would only have to pay him out when she sold the house or died.

Now he needs some money to pay a divorce settlement so the sister has agreed to advance him £50 000 of the £104 000 probate value with the balance to follow later in accordance with the original agreement. My concern is that HMRC will regard him as selling the asset (half the house) at an undervalue (what it was worth then rather than what it is worth now) and he will be liable for capital gains tax.

Is there any way of justifying the payment being based on the original probate value rather than the current value or...