Charlotte,I ran a 1.28 HM as part of running my first marathon this year. Similar advice to above. I did run my tempo runs further - building them up to 6 miles + warm up / cool down. In addition a few of the long runs were overrun (up to 16 miles).
In the build up the max weekly mileage was 40.
I always had the long run set in my mind as the priority.
I think I put too much emphasis on intervals, and not enough on doing a good tempo run.