I agree, I have used a jack hammer before and for once I will let the
digger do the work. I have been assured that, assuming the base of the
garage is not reinforced, a standard beaker for a 1.5T machine should
be capable of breaking through 150-200mm of concrete section.
It makes sense if I can dismantle the thing using an angle grinder and
drag the sections away that would be the safest method.

Thanks

Dug