CGT liability on Flats to House

[anthony m]

Purchased a leasehold flat in 1992 with my wife, lived in it until 2006 and have rented it out since. Flat had originally been the ground floor of a house that was split into two flats in 1960. Purchased the upper freehold flat in 1996 and have rented this out to date having never lived in it. Due to retirement we are considering two options:
(1) Selling the property as is.
(2) Converting the property back to its original four bedroom semi detached state and living in it as our only private residence, selling our current house ahead of moving in.
The ground floor was purchased for 40k and is now worth around 100k, the upper flat was purchased for 30k and is now worth around 80k. My question is: How much CGT can we expect to pay for option (1), and if we go for option (2) do we escape CGT when we eventually sell the reinstated house?
The property is now the only one split into two flats in the street, is easily converted back as nothing structural was done at the time and is mortgage free.

Thanks,

Anthony