Remember, if you can talk comfortably but are slightly sweaty and breathless several minutes into the walk, you're walking at about the right speed. It's a good idea to develop a mental 'effort indicator' in your head so you can ask yourself, on a scale of one to 10, how hard you're working at any point. A leisurely pace might register about a three, moderate would be five or six and hard about eight, for example.

To quicken your pace, take shorter steps. And, strange but true, the faster you pump your arms, the faster your legs will go. Bend your arms at a 90-degree angle at the elbow and think about a shorter swing from your hip to chest. Fast-paced music or a fitter friend can push you to walk faster and may also keep you walking longer.

Week 2: increasing the frequency
Repeat week one, but fit in an extra session to make it up to four days a week. If time is a problem, aim to increase the challenge by walking over more varied terrain. Introduce a hill or two and walk off-road if you can, not just on level roads or paths.

Keep a steady pace and don't allow yourself to slow down going up hills or speed up going down them. Again, keep an eye on your watch so you know how long each route normally takes you, and aim to do it just as fast, or a little faster, each time.

Remember Walking up a 10 percent incline can almost double the energy value of walking, and even walking downhill requires more effort because of the braking effect. Better still, walking on a beach and around sand dunes, where you have to contend with the ground giving way under your feet as well as steep inclines can increase energy output by a whopping 200 percent.

Week 3: building up duration
Repeat week two and make one of your four sessions a longer walk of 45 minutes or more. You can also introduce five-minute bursts of speed during your walks to really raise your heart rate. Follow these bursts with a period of gentler walking for recovery and cooling down, then try another five-minute burst, and so on.

Remember to time how long you need for recovery and aim to gradually shorten this time. Another way of challenging yourself is by walking more briskly between fixed points, such as lampposts, trees or benches, taking note of how many you can pass before needing to slow down. On another occasion you may wish to time how long it takes you to get from one marker to the next, then aim to go 30 seconds faster to the next one, and so on.

Week 4: pulling it all together
Your aim should now be to walk between five and seven days a week, varying your walks using the techniques above. Stick with your programme and keep yourself challenged with the following ideas: