Hi Dodgyken, for clarity, the wiper blade I bought are replacements for the classic Morgan. I bought 8 inch/203mm blades manufactured by TEX. They have a bayonet fitting and will fit the narrow 5mm arm that is fitted to the classic car.
I believe other arms usually have a 5.8mm fitting.
I bought them from Holden classic car parts and they were around 10 GBP each, plus VAT and plus postage.
As Simon mentioned above Car Builder Solutions, who I just used this week, sell a selection of wiper blades. They sell 8, 9, 11, 12, 14 and 15 inch blades.