In the US they would have filed for bankruptcy under Chapter 11[1] and continued to fly while they worked out a restructuring. Most of the major airlines in the US have done this in the recent past: United in 2002, Delta in 2005, and American in 2011. UK bankruptcy law is different and doesn’t give companies this option.

[1] https://en.wikipedia.org/wiki/Chapter_11,_Title_11,_United_S...