Okay just to bore you with an update.
The wheels on the hybrid are the same size as the wheels on my tourer, which is quite handy.
I spent the morning putting the new Marathons on the tourer and the old Marathons on the hybrid. Only one of my schraeder inner tubes was the right size for 700 x 32 tyres (the other two I had were 35s - 40 something).
Halfrauds and the LBS didn't have any schraeder inner tubes in stock for 700 x 32 only presta*. Not to be put off I decided to use one of my presta inner tubes anyway. Seems to be working perfectly fine. As the hybrid wheel is drilled to accept schrader valves, I've "padded" around the presta valve with tissue to minimise any potential valve movement and then put electrical table around it to stop any dirt getting in. Took it out for an 8 miler and didn't have any problems. So this set up should cover me until my new inner tubes arrive.
*having looked at the tag that came with the new Marathons it says 32-622, 28x1.25 700x32c on it. Does that mean 28x1.25 schraeder inner tubes would do? I take it that is the measurement used for MTBs.