Thanks everyone!!
I think i'm now thinking i'll go for the ferry option. It's the one D wants me to do!
Jumbly - we spoke to our friend about his landrover. It's still not fully operational (or clean!) and he just doesn't have the time or money to be doing it at the mo as his wife's due to give birth to their first baby 2 weeks before the wedding and he's trying to get the house done too. Plus it complicates matters of how she gets there. He was a bit upset but we've talked him round (it's the right thing to do) and means he, as one of the groomsmen, gets to travel with the boys in D's landrover and can do the usherly duties 
Lets just hope it's sunny!!!