Had a read through some of that and came across this, which seems to be on my side, however isn't worded as a share value -
"Condition C - the purchaser owns an interest in another dwelling which has a market value of £40,000 or more and is not subject to a lease which has more than 21 years to run at the date of purchase of the new dwelling"
This part is however worded as a share value, however it's talking about it being worth more than £40k -
"If an individual is a joint owner of another dwelling then they may meet Condition C if the interest in land is a major interest not subject to a lease longer than 21 years and the interest that they hold is worth more than £40,000."