CGT fiddle ? on second home

[TCHS]

A nearby house got bought 5 years ago for around 150K and has stood empty since. The owner has tried unsucessfully to get planning permission to extend it several times. It is unhabitable as work stopped as soon as the first permission was turned down. The owner has his tax details, companies house address, electoral role registration etc, noted at the house so porports to live there but never has done. He has another place locally. The unused house is now worth 250K, but 400K done up with a small extension relatilvly cheap refurb / extension. If sold soon, is the owners CGT liability likely to minimal or should his position be reported.

[TCHS]

Can anyone say if the three year rule would apply on a property that has never been ones main residence, or does it apply to all properties. Also - does indexation take place from the date of purchase up to the value 3 years before the sale, or starting after 3 years up to the time of sale. - thanks.