CGT on PPR when running a business from home?

guys, im not too failiar with this... you might be able to help .
My father is self employed and works from home (uses one of the rooms as
his office ) . He recently had a visit from the revenue who ,at one stage remarked that if the house was ever sold this room would be liable for capital
gains tax .

Is this right ?

If so how do you calculate how much would have to be paid ?

Thanks a mil

Re: visit from the revenue

Yes, it is correct.

The charge will be based on the proportion of the house used in his business and its duration of use.

Re: visit from the revenue

Section 5 of the Revenue Guide to CGT gives an outline of the partial PPR CGT relief that might apply in such a situation. If in doubt get independent, professional taxation advice. His accountant may be able to assist.