In reply to misterb:
"I have just done 2 long runs so far of 20 and 21 miles at 10.15 (too slow) and 9.15 pace respectively which felt ok but i am unsure really of the pace i should be running as the distance gets longer "
I'm not sure what your '10.15' (too slow) comment means.
My advice is that you can't really go too slow on your long runs. Without really knowing how hard you're running your 6-10 milers, then 10.15 seems okayish for your hard run. By way of comparison, if 9.15 the right long run pace, then i'd say your 6-10 milers should be down about the high 7, low 8 pace.
The aim of the long training run is what it says on the tin- to go as long as possible. If you had a choice of using your available training capacity between 20 miles at 9.15, or going a bit slower and doing 25 at 10.15, then the 25 at 10.15 is the one to go for.
If you're 4 months out, then don't be thinking about pace yet-most coaches agree that pace is what you work on when you can do the distance.
BTW, Anton Krupicka says the one thing he wishes he'd known when he started out was that he could have done a lot more walking in his training... don't be afraid of it!
Post edited at 10:51