Hi Julian,
Sometimse when I respond to newbies efforts with an honest response, people think I am negative - I think they suppose I should just say 'nice effort'. However I seek to help and coach, so please take the following positively.
The hackle is fine, althoug maybe just a tad too long.
I am pleased to see that you did not crowd the head of the fly.
I think the body could be more even from butt to head - but is OK.
Mainly I would suggest that the back of the fly stop above the barb of the hook, though this one looks good and will catch fish.
Press on, press on. Good luck, Greg