Not sure on something?
Rollover relief is only available on the disposal of assets that are used for the purpose of a trade. Although profits of a rental business are calculated in the same way as a trade the letting of property is generally considered not to be a trade.
It is possible to claim rollover relief on properties used for the commercial letting of furnished holiday accommodation as this is considered to be a trade.
Whether a trade is being carried on is a question of fact and is to be decided on a case by case basis. Case law dictates that this is very difficult to establish.
So the answer to the original question is that this client will not be able to claim rollover relief on the sale of his rental property unless he is carrying on a furnished holiday letting trade from the property.