Sarah - I was looking at your paces you got from RW. I think they sound pretty good. We need to put MP in there, which will be about 7:45 - 7:55 and HM 7:00 - 7:10 for training purposes.
I did a session today for the first time this year and its one of my favourites. 4m w/u followed by 45 mins of 5mins MP / 5 mins HMP continuous. Using MP as a recovery to something faster really makes it your friend and I think it would be a session you would enjoy. We could add something like that into Tuesday's session? Then your 20 next week should be run at a nice easy pace because you've got the 9 mile race on Sunday, which I'm assuming will be flat out?
The following week I think you should put some blocks of MP into your 18m, say 4 easy/ 4 MP/ 4 easy/ 4 MP/ 2 easy.
Then we can look at how you're going to approach the Hull 20 depending on how you feel closer to the time?
The weeks will come in quite fast now but you're right on target and everything is falling into place nicely. The taper can be used for a fair bit on MP stuff too.

Edited: 21/02/2013 at 22:10