I'm not fit, I'm too heavy but I'm also no slouch

Hi I'm new on here,

This site was recommended to me by a friend in my department who is one of the fittest men I know. I should start by saying that I work Estate Security. This translates to the fact that even though I do little to no targeted exercise I am on my feet during a working day for about 10-13 hours. The muscles in my legs are terrifically strong and there en-lies the issue.

I am on my feet that long which means most of my days off go into recovery. If I wasn't a beginner I doubt this would be an issue but I am. Also I am a large build (Rugby scrum half/stocky) with the additional problem of excess weight. I'm 6'3 and weigh about 120 KG.

Finally I want to apply for other jobs but they require me to be fit and hence I questioned my mate and he sent me here. So can anyone recommend a workout that is fat burning, not overly strenuous on the knees or ankles and yet effective enough that I could lose about 20KG in 6 months? I've got my diet fully worked out and its going great but now I need direction.

I'm not bothered about being ripped, I'd just love to be lean. Right now I just want the weight gone while doing a physically demanding job.