overseas flat under Installment Sale

I bought a flat in my home country under from a developer under Installment Sale from 6 years before moving to UK Installment Sale means: You acquire the property in installments, but the title or ownership is not transferred until all payments are made. in this case I don't have permission to sell or rent it till I paid all the installments and if I didn't pay two consecutive installments the contract will be cancelled, in this case my home flat isn't a full ownership and I can't sell it till all the Installments finish after 4 years I want to buy flat in London in this case in which tax category should I be first home buyer or second home buyer?

Hi,
Please have a look at the guidance at SDLT29845 on the definition of a first time buyer.
SDLTM29845 - Definition of a first-time buyer FA03/SCH6ZA/PARA6
As this is not a personal tax matter, we cannot provide any advice.
Thank you.