Notional CGT on a leaseholder owned company

I have letting agency client who manages blocks of flats. His solicitor emailed him the following:

"Accountants now take the view Revenue consider there to be a notional charge to CGT on a leaseholder owned company where the Company grants lease extensions for no consideration to the tenants who own it. This is because it is separate legal entity and even if there is no money changing hands, there will be a charge on the notional value that would have passed if it had been a lease extension at arms length and money paid."

Is this the case? If so how would CGT be calculated?

Thanks