You have to read carefully on the inner tube box yourself, as to which tyre size they are for.....Sometimes I find it to be not very obvious.....That last point Andy might have some relevance. I keep getting new tubes from Halfords and ask for those suitable for the Crossfuse, and they seem to give me different sizes every time. The tyres are I believe 700C 35 so what inner tube size is the best to buy for those. And the Marathon Plus tyres seem to come in 700C by 35 and 700C by 40 so I'm guessing I order the former?
Best of luck