Afternoon Ash,
I wish you were a bit nearer here so we could go for a ride and see if I can help. You've had a huge dollop of advice here and it's all good. As a Senior Qualified Observer with the IAM in a former life I'd commend getting in touch with the local IAM bike group. TVAM used to be very big and very active darn sarff. My step-father was instrumental in setting up the Solent Advanced Motrocyclists
http://www.solent-advanced-motorcyclists.co.uk which might be nearer to you. The IAM can be a sententious bunch of prats but they do a lot of good work and have a lot of talented riders who do the training. If you don't like the person who you are offered first as an observer ask for another one. Most groups have a number of observers and will try to put like minded souls together.
From what you are saying you have got into a downward spiral of loss of confidence leading to excess tension leading to the bike feeling crap leading to a loss of confidence...
Been there, done that. I fell off when I encountered a patch of gravel on a corner in Scotland in 2005. It has taken me a long time to get my confidence back.
First: forget speed. Ignore it totally. It doesn't matter. What you need to do is go through corners at a speed you're comfortable with.
Second: forget what everybody else is doing. It doesn't matter. If you are riding in a group then it's a group ride and not a blast or a race. Faster riders should be able to ride at any pace and, if they are good mates, they should be able to ride at a speed that makes you feel comfortable and not scare the shit out of you.
Third: approach a corner at a speed which allows you to see and read the corner in plenty of time to set your bike up correctly. Slow in fast out every time. Always ride at a speed that allows you to stop safely on your own side of the road.
Fourth: as part of the assessment look for entry, apex and exit points. Moving your position on the road will help you to see more of a bend i.e. start near the lh curb for rh bends and vica versa. Once you can see your entry, apex and exit points link them with the smoothest, gentlest curve possible.
Fifth: having assessed the bend look where you want to be, the exit of the bend or if it's a tight bend the limit point. i.e. where the two curbs seem to meet. If you look just in front of the bike you will 50p piece the corner as the bike will change direction everytime you change where you're looking.
Sixth: as you will be riding slow in and fast out keep a gentle positive throttle going round the corner. Cornering takes energy from the bike. If you coasted round a flat corner you would slow down therefore you need to add some energy to the bike and push it round.
If you feel out of control entering a corner you are possibly going too fast FOR YOU ON THAT DAY. Try a gear down for the next corner to give you more engine breaking and more throttle flexibility.
You said at the start that you weren't feeling 100% when you went out. That probably didn't help. If you are tired or ill you will tend not to look far enough ahead to ride smoothly unless you really make an effort.
In short; start by riding slowly but smoothly. Once you feel comfortable increase the pace gently but don't stress about it.
I hope that helps. If you really want bring the family to Scarborough and I'd gladly spend some time with you if it would help.