I forgot to update about my session with the powerlifting coach (hope it's OK to use this thread as a bit of a diary, but also some of this might be interesting for others!)
He completely demolished both my squat and my deadlift - luckily we didn't have enough time for bench.
My squat: my stance is narrow and my squat is quad-dominant. My hips aren't open and my knees are forward rather than out. This is all fine as far as it goes but as the weight gets heavier, this is putting too much stress on my knees and not loading my hips effectively (hips are stronger than knees). To get stronger in the squat I am going to need to use a wider stance with my toes more out to engage more of my glutes and outer quads/hamstrings.
I did a few sets squatting as per his adjustments during the session and it felt horrible. Mainly because even though I thought I was getting better at activating my glutes, they are still basically rubbish. So I'm going to have to take the weight right back and build up again from the beginning; but I'm interested to see what happens.
Deadlift:
We did a few very slow reps and he had me dropping the bar when it was just below my knees. When I dropped the bar I stayed perfectly balanced. Apparently this shouldn't happen. I'm not engaging my posterior chain properly (glutes again! hamstrings again!) - if I was, I would tip backwards without the weight to counterbalance me. So we spent a fair old while working on setting up in the right position and activating my hamstrings, glutes, lower back and lats so that I'm like a coiled spring before the bar comes off the floor. This was great and I immediately felt the difference.
So all interesting stuff - lots to work on, but I like that. I'm seeing him again in a week and a bit.