It was definitely live. Honestly most of their performances this era have been lip synced but this definitely was not one of them. Notice the breathing, and dynamics that you can actually hear changing as they move the mics. Plus there were moments when Jade was flat and Leigh was rough, which they would never allow.
Yeah I wouldn't like to swear to it being 100% live but it definitely was for the most part. Jade hit a dodgy note at one point which surprised me as she's usually flawless. But I thought Leigh sounded great. A lot better than Jesy actually.