Look at this picture. eleven men, one Roll Deep. Do you know what that says to me? It says here are eleven fellas who probably spend quite a lot of time queuing in order to do their job, or waiting to have another go, once theirs has finished. They might cover it up with an arm in the air or two, a walk from one side of the stage to the other, a moody stare into the crowd, some bouncy high-fives, and a certain amount of joining in at the end of each line, but when you get right down to it, it's all just queueing.
And to make matters worse, sometimes the queue is barged by a singer. Someone who isn't actually even IN Roll Deep. They've be brought in on chorus duties, taking precious rhyme time away from people who've been in the queue for ages, actually. It's not fair, just because they can provide some melodic light relief from all of that truth-spitting, that they get to stroll right to the front. That's basically added an extra thirty seconds of arm waving and an agreeable "yeah yeah" or two, right there.
So don't be surprised if you notice that some of the more backgroundy Deepers are subtly shooting daggers at Alesha during her bits. They're only worried that they won't get a go on the mic.