Nothing to do with state aid or the EU. It's a public procurement deal we signed last year with the WTO which gives the UK access to 1.3 trillion in overseas Govt procurement.
It excludes defence contracts and as this ship is going to be managed and crewed by the Navy, that could potentially be used as a loophole, alternatively they could base the hull design on a type 32 destroyer.
Nobody knows the outcome yet so I wouldn't waste to much time howling at the moon.