Thanks everyone for the advice.
I'm now going to change my plans (Mainly due to Indalo)
I was going to buy two Freego Hawks and stick them on the back of the Starburst but at 22kg each I'm going to have to lower my sights. Carry on looking!!!!
Rang a dealer who'd written it down in his little black book so I can answer my own question.
It's 120cm. The rail on my fiamma bike rack is 128cm so it's a bit close. Extensions I think.