CGT on Private Residence subsequently developed as building plots

Since December 1999 my wife & I own a property abroad on 2700m2 (below the Permitted Area of 5000m2) . We lived in the house for 100 months as our primary residence (we were tax-resident there) thereafter let it periodically and at other times used it as a secondary residence. The house was demolished in October 2022 and the 3 building plots created are to be sold imminently. Are we eligible for Private Residence Relief, and how is it calculated ? Until the date of demolition, or to the date of sale ? Am I correct to pro-rate the allowable costs on the proportional size of the plots ? Thank you

Hi,
Private Residence Relief applies on the disposal of a dwelling house which is or has at any time in the person’s period of ownership been their only or main residence. In order for Private Residence Relief to be available, there must be a “disposal of a dwelling house”. You can see guidance here:
CG64200 - Private residence relief: introduction: scheme of relief
So if a house was demolished and the land sold later, relief would not be available on the sale of the land.  
Any allowable costs should be apportioned between the plots of land in a just and reasonable basis. Please see the guidance below:
CG14771 - Introduction and computation: computation: consideration for disposal: Apportionment when assets disposed of in a series of transactions
Thank you.