Hey! Thanks for the email, always cool to hear from a fellow Englishman haha.
First off, cool stuff! Impressive improvement is always fun to look at. You have come along a lot in the past couple of years. You specifically mentioned a few things you wanted to work at in your email, brushwork being one of them. Right now I personally think that is one of your strong points, and in the long run something pretty superficial and always easy to improve on (relative to other things). Basically what I'm saying is that I wouldn't worry too much about it, you're off to a good start. Just try to think about why you place each mark in a certain way, what are you trying to describe about the object etc.
What you really wanna get into the habit of is drawing, a shit ton, and without worrying about rendering so much. No amount of rendering or brushwork can fix a bad drawing. By drawing I mean the actual important principals of laying out an image, everything from anatomy and perspective to composition. Don't stop rendering and painting stuff but try to set aside an hour or two a day to just draw.
Do you draw from your imagination a lot? It's one thing to study a lot, but this time goes to waste a little bit if you don't meaningfully try to apply the lessons you are learning to your own personal work. I see you have some really cool multiple angle portraits and figure drawings in here, try making a few without photo ref (I'm presuming they are referenced, if not, awesome!). I can't stress enough how important drawing from imagination is for me in pushing myself. How else can you really test what you are learning in a deep enough way to visualize it directly.
I love the life studies and all the first person perspective stuff, keep all that up and lets see some personal work, some things that are less of a study. Doesn't matter if they turn out shit, just see them through to the end and really try to finish things. They will get better and fast!