Thanks all, that's pretty conclusive. I'll double check with the schools I'm considering, but like I said above my local FTO doesn't seem to consider it a problem.
Thanks also for further advice on my 'plan'. I managed 45hrs for my PPL in 4 months so don't see why I shouldn't get through the CPL in the same time or shorter in terms of weather, a/c and instructor and my availability.
I also understand what people are saying about continuity, though at the end of the day I'm not aiming to be CPL standard just for my test day - it's the standard I'm trying to apply all the time and this is the way I'm approaching hour building as well. If my developing skills were to just fall away after the course then that in my view would be the biggest cost to me. At the end of the day I need to build it around a full time job so the decision is made for me.