Glutes/hips my downfall - suggestions?

Hello hello

My story so far: runner for 6 years, have run about 20 half marathons (PB 1.35 set in March 2011) and 3 marathons (PB 4.14 April 2010).  I ran VLM 2011 in a disappointing 4.24, after following a 3.30 training programme pretty well.

I don't have strong hip flexors/glute muscles.  This has been pointed out to me recently by a physio.  In London last weekend I felt in the later miles that my hips just weren't powering me forward, my back was hunched over and all power was through very tired legs.  Not ideal.

I don't think my body can cope with the high mileage.  I've got the speed in the shorter distances (5k PB 19.42) but I have a feeling that unless I improve my core/hips/glutes then I'll forever just fall short of my marathon targets.

Does this ring bells with anyone?  Can anyone suggest what I should be doing to improve my strength in this areas so that I improve my form and ability to run marathons at my full potential?  Would pilates help?

Any suggestions would be most welcome - I am desperate to run a marathon well, I think I should be capable of a sub 3.30 but so far I've been way off.  I fear that unless I tackle this issue, I wont be moving forward.

well do some glute/hip strengthening exercises then?

Clam is a good one....'good mornings' also.

Lunges

As before clams, single leg squats concentrating on form and balance over depth, rear leg extensions with a power band, leg raises when lieing down on your side with the working leg 10-12 inches behind the static leg.

 It's very difficult to describe the exercises but ig you google there'll be plenty of videos about particularly on youtube