Thank you very much for your detailed reply. I really appreciate it. I actually tried the multi-cut tool approach before posting here but thought there must be an easier way. I've since looked at the Lattice tool as well which gives a similar result. I've come to Maya from Sketchup, and a lot of the easy stuff on there is a nightmare on here! But I can already see just how much more control Maya allows for objects, so the learning curve is paying off... very, very slowly!

Thanks again, very good of you to help