A group's interest capacity is the aggregate of the interest allowance of the period and any unused interest allowance brought forward from an earlier period that is available in the current period of account (or the de minimis limit, should that be higher).
The carry-forward may be restricted through time-expiry. In essence there is a five-year rule.
Normally, interest allowance can only be accessed by the worldwide group in which it originated. There is a limited exception to this which may have effect where a new holding company is inserted between the ultimate parent and its shareholders, see CFM98245.