Congrats, hope it all goes well. I've done a couple of ACs in the past and have gotten offers. If you have a group task I'd say the main thing is to be involved but also show that you're a team player (e.g. ensuring everyone gets a chance to speak, asking meaningful qs). If not I'd say just be yourself and study the company as well the field you are going into well and you'll do fine. I'm yet to hear back, hoping they're just taking their time for the London consulting.