KyleRB,
I think Brigantee is correct. Delta were only able to purchase 49% of Virgin Atlantic and Virgin are a not public. I believe that EU rules limits non EU based companies to no more than 49%, however another EU based airline could invest more.
Happy to stand corrected if wrong. Until Brexit is complete the UK is still very much subject to EU rulings. I doubt the UK government would want to change the investment rulings anyway.