The Physical Activity Guidelines issued by the U.K. Department of Health recommend at least 150 minutes per week of moderate-intensity physical activity—think of it as 30 minutes, five days a week—for all adults, even the elderly and disabled. However, you don't have to do all 30 minutes in a single daily session. In fact, the newest guidelines allow you to count all moderate intensity physical exertion throughout the day, even if it's just a few minutes at a time.
You can also reach your goal by performing chunks of exercise in 10- or 15-minute blocks throughout the day. For example, do 10 minutes before breakfast, 10 minutes during your lunch break, and another 10 minutes after dinner. Or do 15 minutes in the morning and 15 minutes in the afternoon. If you're just starting out, gradually build up to 150 minutes a week.
If you're already exercising and fit, you can cut your exercise time in half—to just 75 minutes a week—by doing vigorous exercise instead of moderate. Generally, that would amount to 25 minutes, three days a week. Or, you can perform an equivalent combination of the two intensities, with each minute of vigorous-intensity activity equivalent to two minutes of moderate-intensity activity.
If you're able to do more, that's even better. The Physical Activity Guidelines specify that you can derive more health benefits by boosting your workout time from 150 minutes a week to 300. But the most important thing is that you do something