Thank you for your question.
If your son is the only owner of the property then there is no extra stamp duty to pay as the property would be registered in his name and also this being his first residential property, extra stamp duty is not applicable.
You could draw a legally binding agreement that he would return the initial capital outlay on the sale of the property. As far as the gain on sale is concerned he could gift you that sum.
IHT implications -
If you loan him the amount, then it remains part of your estate for IHT purposes and the 7 year IHT rules don't apply. If you gift him the money, then it is treated as a potentially exempt transfer and 7 year rule applies.
If your son gifts you what is the eventual profit on sale of property, then it would be a PET for his IHT purposes.
If your son lives in the property throughout the period of ownership, any gain made on sale of it would be exempt from CGT as it would be covered by private residence relief. AS the property would be in his name I have covered how you should handle the transfers in a tax efficient way.
I hope this is helpful and answers your question.
If you have any other questions, please ask me before you rate my service – I’ll be happy to respond.