Hey!
I had a bit of a dip last week. After a strong 11 mile run, followed by a good 4 miles, my muscles seized up, I think I was fighting off some kind of bug thing, and the rest of the week was wiped out.
However, I made a good return on Sunday with 13 miles! I really did not expect to be doing this distance just a month into the year. I build miles v-e-r-y slowly!
The week blip even had me doubting the marathon. I mentioned this to my husband though and he was surprised. He convinced me that I could do it (by not even really saying anything other than suggesting he thought I could do it) so it's back on! I'm so fickle.
6 miles done at lunch time today - very very cold in the shade, but bearable in the sunshine. Planning 4 miles tomorrow morning, but it looks like it is going to be -2..... oh well. I have layers! Then running into work on Friday 9 miles or so. I will then rest on Saturday, and probably do long run on Sunday. Should be able to get it up to 2.5 hours, and hopefully a smidge over 13 miles. Not sure on a route yet. I need to rearrange my week so I can just add on to my commute run, but it just hasn't worked out yet.
Mikasa - September is soooooo far away! Why not build up to the distance for Spring (the Stratford Upon Avon half is at the end of April - as part of the full marathon, which I'm doing!), and there are half's in Torbay and Paignton in June. You could build up your miles for April and get an idea of how much work you have to do to get that 'race' time. Then you could have a 'maintain' period, with a regular long run of 10 miles or so, and other running around it, and see how you are feeling in June with more miles under your belt. And then focus on some sharpening up for September. Or October if you went for the Cardiff half 
Why do one, when you can do three??!?!??? 