Many thanks to all, I'm back and not too damp.
We were lucky in that there was rain on four days out of 5 but only on a couple of days did it really pour down and then only for an hour or so.
I managed with midlength sealskinz and baggies (it was not cold so the legs did not suffer. ss jersey, lycra armwarmers (dhb from wiggle) and my convertible jacket. Again it not rainning for hours on end meant I could use the jacket as a gilet and balance being wet from the rain against being wet from the condensation.
helmet with Z cotton cap underneath and, yes, shower cap on top when it was really bucketing down (just remember not to cover all the rear vents

)