Furnished Holiday Let

Hello

I do apologise if this is some what of a novice question however I would appreciate any assistance that you can give me.The wife of a client of mine ran a furnished holiday lets property in which they also live. The wife passed away (last tax year) and the property was left to my client. It is still currently being run as a furnished holiday let.We would like to know for tax purposes when the property is eventually sold say in 3 years time, what would the base cost be for tax purposes, i.e. when it was initially purchased by the wife of my client or when probate was finalised.Secondly, I understand that the rentals can be taxed as a Sch A or a Sch D1 income, my client does not make losses in the furnished holiday business and has no other income, so he is happy to treat it as a Sch A income to reduce the amount of national insurance due. However again for disposal purposes is there any benefit of treating the income as Sch D1 instead of Sch A.  Many thanks