Thanks for info. Martin ... maybe I'll make them a bit thinner for bending as they hardly get "used" as rubbing strakes so they're mostly cosmetic cover for hull to lid join.
A couple more "bits" out of the long story: While searching "5.1m hardwood" I eventually rooted out 5.1m Balau decking fascia form Goole. Standard shipping cost made it a bit pricey for one item but I bit the bullet and ordered. When it turned up it was in two pieces

. Supplier agreed to exchange then said it's no longer stocked so will collect and refund(yet to happen).
Spurred on by getting so close I decide to spend one more day scouring "decking" as no wood yard would supply 5.1m. Eventually I hit the jackpot

. Chiltern Timber could do me
http://www.chilterntimber.co.uk/product/keruing-half-lap-lorry-trailer-decking-22-x-140mm/ .... And they have it in stock ... I checked with a real person who looked

. So guess what little detour I'm making on the way back from Oxford in a couple of weeks.