It's all good advice Mr. Hicks. I swapped my PPL logbook for a commercial one at the end of my IR, and with hindsight I should have done it much earlier. I also use an electronic version (Safelog) as a back-up and to check my adding up. It's also very useful for printing reports and totalling different types of hours (which you'll need to do for job applications).
As potkettleblack says the CAA form for issuing a CPL / IR is as complicated as the test itself. If you're anything like me, your brain will have melted by then, so a combination of electronic and commercial logbooks will make life much, much easier.