Cambridge can't be done online. Also CDC's wont take you on unless you're above BMI of 25+. So I think you're going to have to think of an alternative hun. Exante can be bought online and is basically the same thing. Or you could do calorie counting.
You wouldn't be able to follow the VLCD plans of ss or ss+ as you are in the healthy range BMI wise but as long as there are no medical problems or medications you should be ok to do the 810 plan to lose the weight you wish to lose and 9st is still within the healthy range for your height .