HMRC is unable to comment on French customs authorities custom requirements.
From the scenario outlined, import VAT and duties will be due on the purchased vessel when it is imported into the UK for the first time.
You may be able to claim preferential duty rate under UK-EU TCA on entering the UK, please see the link below:
Rules of origin for goods moving between the UK and EU
Further guidance on pleasure crafts coming to the UK and custom requirements can be found in the notice below:
Notice 8: sailing your pleasure craft to and from the UK
In regards to Temporary Admission (TA), if the vessel is registered in the UK and the owner lives in the UK, from the information provided, TA may not be applicable as this will not meet the eligibility criteria, please see the following link:
Reference document for Temporary Admission: eligible goods and conditions for relief
In regards to Returned Goods Relief, goods returning to the UK may benefit from import duties relief subject to conditions, please see the following:
Pay less import duty and VAT when re-importing goods to the UK