Thanks for the many good tips.
Hired a self powered concrete breaker found using the Stihl saw did not
speed the job up but good for getting a straight edge.
The first 4 square feet took two hours most of that trying to remove a very
heavy breaker impaled right through the concrete-luckily it was not
reinforced.
Speeded up tremendously after learning to take little bites at a time and
broke out 8 foot by 4 foot section in 6 hours with tea breaks.
Concrete breaker hire was £42 for a day or £100 for a week.Just got it for
the week as I have a 450mm inspection pit to insert in the pad and a drain
to break out.