I wouldn't worry about yesterday's HM time too much, as you hadn't tapered. You'd have probably knocked a couple of minutes off, which would have you at almost exactly 3hr marathon pace, according to the RW racetime predictor.
Looking at your training history, it's dedicated for sure. I think that there is not enough variation in your pace. Almost all your runs are done in a fairly tight band of about paces. I think some of your shorter runs should be faster, and some of your longer runs should be slower. (although the graph is perhaps hiding some interval training, where average pace wouldn't show it up).
I can see your long runs are beginning to build up. They need to be a focus during March. They should also be slower IMO. As painfully slow as it seems, try 8:45 or preferably 9 minute miles for the LSRs. That should be the session that concentrates on building your aerobic capability (your other sessions can deal with speed and LT etc). And by keeping it slow, you can get more "quality" out of your quality midweek sessions.
IMO, you have every chance of hitting 3 hrs in London. But have a think about the comments I make... and hopefully others will also give opinions. Good luck.