I'm very good at putting things off, so I would prefer not to have to wait - do I have to? or can I just start?

There is no hard and fast rule as to when you should start a new program. Do you start your new exercise regime on Monday, or should you start on the day you decided to make some changes? Personally I wouldn't wait until Monday - things can and do happen to a person's resolve if they wait for too long. So if you have made a commitment to yourself to get fit and healthy, then today is a good day to pick up the phone and make the call.

However, there are some caveats - if you are very overweight, you might like to get the all clear from your doctor first. But you can start small - how about walking to to the doctors instead of taking the car or the bus. Climb the stairs. If you work in a high-rise building, get out one floor before your normal stop and walk one flight - as you get fitter, you can walk more flights. As your strength and stamina improves you will begin to see some changes and you will want to continue.