I don't know anything about Cambridge or 5:2 or anything like that. I've lost six stone fairly slowly over the last few years by eating a diet low in complex carbs (potatoes, rice, bread, pasta etc) but high in other veggies, with small amounts of meat and dairy.
Everyone's different, but I have to do some exercise (mostly 10-30 mins walking per day) if I want to lose weight.
Like most people I go off-diet occasionally (birthday cake, christmas pudding, hard day at work which leads to chips and cheese). I try to take a sensible approach to these things: enjoy carbs like they're my last meal, but then tomorrow is another day.
As long as I don't eat complex carbs more than three days in a row (and no more than once or twice a month) it doesn't impact on my appetite or my weight. I find I'm much less hungry in general when I'm not eating complex carbs. What works for me might not work for everyone, but it might work for some other people.
The bottom line is that losing weight and keeping it off means changing how you eat FOREVER so you have to find things you enjoy eating that work with your metabolism. I'm happiest eating steak with cream and peppercorn sauce, and as long as I don't eat it with chips or croquettes or any other form of potato, I keep losing weight.
You need to figure out what works for you. When you find it, it will work.