I was able to get tickets to The National and Fat Dog/The Dare/Desire this year pretty easily once they went on sale. I do remember people having issues though and lots of people looking for tickets week/day of the gigs
I could definitely see it. I think they're great live, seen them with my Dad a couple of times. Southampton -> London with a day in between definitely leaves a decent chance, especially as they'd only be doing 45 minutes in the day time.
1st time going to mad cool this year(went to see Pearl Jam) and despite the sound stage not being the best one and the probably the worst crowd i´ve ever seen at a concert (people were just speaking to each other during pearl jam unbelievable...) everything else was great and if the bands are good enough its one festival im consider going.