Julie says: This is a great question. Virtually everyone is safe to exercise but it is best to check with your GP if you have any health conditions which may effect the type of exercise you should do.
Gentle to moderate intensity exercise is generally safe but there may be certain things you should avoid such as bending too far forward if you have osteoporosis in your spine, crossing your legs if you have had a recent hip replacement, or trying to balance if you suffer with dizziness.
In my experience and having taught thousands of people, it is extremely rare that anyone is told not to exercise, although they may be advised to avoid certain types of exercise.
You will find that all good instructors will ask you to complete a questionnaire before you begin a new class; this is for your safety and also for their insurance. As most GPs are so busy you can probably ask the Practice Nurse for advice to help choose an activity that is appropriate and that you enjoy.
The worst thing we can do is sit still for long periods of time so getting the go ahead to exercise might be the best thing you can do for your long-term health and wellbeing.