Ms Williams recommends a balanced exercise regime to help you lose weight and achieve the perfect bikini body. Cardiovascular exercise - such as jogging, brisk walking or skipping - is important as it builds up a sweat and gets your pulse racing. The expert also recommends yoga "for improving flexibility and as an add-on to other forms of exercise".
As well as its benefits for flexibility, yoga can help people to relax thanks to the breathing exercises and stillness. However, Ms Williams emphasises: "I wouldn't suggest it as a sole means of getting in shape."
For those who are trying to get summer ready in a short space of time, the fitness guru recommends thinking about exercise from the moment you wake up. Fitting in small exercises and moving about throughout the day can produce the results you're looking for in no time at all.
Ms Williams suggests: "For example, you can literally run up and down the stairs and take things up and down the stairs every day before work as many times as you can - that really will count. If you have a little tracker you will see the results, and I think that works for so many people."
Other simple ways to fit movement into your daily routine include squatting while you brush your teeth and walking briskly to the bus stop. A good way to tone up your arm muscles is to leave the trolley behind and carry two baskets around the supermarket instead.
You could even create a small fitness routine to complete whenever there's an ad break during your favourite television programme or you're waiting for the microwave to finish cooking your supper. And a few minutes of skipping or some tricep dips three or four times a week could also produce rapid results - even in time for the summer, if it ever arrives!