Well done for biting the bullet again, Kevin. If you're doing London in 2003, now's the time to begin!
My experience in London this year wasn't unlike yours. From a cold start, I trained like a demon from late September till January (schedules, schmedules...), got injured, recovered, got injured again, and did almost nothing between February and April. Turned up at the starting gate anyway (a lot of sponsorship money was resting on it), skipped through the first half in around 2hrs 15min, and...well, by 14 miles I was taking walking breaks, by 18 miles I was walking, at 20-ish miles the "get-you-round" group galloped past me (I tried to keep up but failed) and my last two or three miles were 40-minute miles which I completed only by promising myself that if I finished this time I would NEVER have to do another marathon. Ended up with a time just a fraction under 6 hours.
Keep us updated. Plenty of us have indulged in a spot of recidivism from time to time. Enjoy your running and you'll probably find that after a while you won't want to poison your body with cigars anyway.