Hi Vince.
I also fly a CTSW, so I'm genuinely interested to learn from this incident.
When you say
10 litres measured at straight and level was quite enough for Dundee.
Can you confirm that you calculated your fuel burn as being 10ltrs between Barrow and Dundee? Just a rough measurement suggests the distance as being 140nm on a direct track. Assuming a cruise of say 110 knots using 14ltrs per hour I'm struggling to see how 10ltrs could be adequate. Does the 10 ltrs include or exclude the 6ltrs unusable (the aircraft I fly has this clearly placarded).
Also, what type of flight display was fitted to your aircraft. Was it the Brauniger AlphaMFD 'LCD' style display or the Dynon EFIS system, (the latter will show fuel to destination if coupled to a GPS). Both systems however do not directly measure fuel in the tanks - they rely on the pilot setting the onboard fuel level prior to flight based on dipping the tanks. When were the fuel tanks last dipped? I'm curious about this as you mentioned that you 'diverted along the coast to land at Barrow' - Did this use additional fuel? Barrow does not normally have either MoGAS of Avgas available.
Thank you.