There could be some light sprinkles around in the morning for the support races, but I think the bulk of the rain will start to move in early in the afternoon, probably between noon and 2 pm. Periods of light to moderate rain will likely continue for most of the race. I don't think that the rain will be so heavy that the race will need to be stopped. The rain may become more scattered in the closing hours, and there may be a few breaks in the clouds as well. I expect that the total amount of rain will be between 0.08 and 0.15 inches (2 to 4 mm). It will be a little breezy all day too, with a west wind of 10 to 15 mph in the morning and early afternoon shifting to the northwest. Gusts of 20 to 25 mph will be possible at times.
I won't be able to provide live weather updates during the race, as I will be spending time at church and with my family to celebrate Resurrection Sunday.
Here's a link to radar for the UK.