We're a few miles down the road, if it stays dry you may be OK as you're quite high up there and it seems to drain as well as it does here, but I'd say doubtful - we've had nearly 6 inches of rain in the past few days. Our top paddock is unrideable (unusual) and I think will stay the same for at least 2 days of no rain - but the problem is that more rain is predicted.
Just an update - sun out all day today, and our top paddock is definitely now rideable. So long as the weather is not too wet tomorrow or Friday (ie light showers only, no more of this silly torrential stuff) I would have thought you should be OK. However there is rain (showers) forecast for Thursday and Friday as well as over the weekend, and quantifying the amount of rain seems to be a problem for the forecasters, so I guess you'll just have to keep in touch with the organisers and wait and see.