Group loss relief

Hello, I have a query on group loss relief which is probably best explained with an example. Please assume the following: Company A owns 90% of Company B Company B has trading losses of £100,000 Would the maximum group loss relief available to Company A be £100,000 or 90% of £100,000? In the BPP practice and revision kit there is a similar scenario to above and the full £100,000 is available. It would seem odd that a company can claim loss relief on a loss which isn't really theirs. Thanks