My sincere thanks to Andrew and Len for their advice. I have decided on a
5HP 4 stroke and will be comparing prices soon.
May you prosper with your gardens.

Just Me

I would stay clear of electric ones. I know that some people out there may
have them, and they work well, but it can depend on the type of prunings
you
are mulching.
People might argue that the electric are more quieter but when you are
using
a machine that noise comes from the engine as well as the job you are
doing
(ie mulching) then it doesn't make a huge difference.
I would also guess that while a horse power rating could be equal between
electric and petrol, the petrol would possibly have the advantage with
torque which would play a big part in a mulcher as it is under load and
the
jamming problem you had could have been due to lack of torque.
Sorry I can't give any make/model, but lens advice seems pretty good, and
I
can only agree with suggesting petrol engine, and possibly allow for
slighter bigger diameter of prunings than what you think you need.
Try getting the dealer to demonstrate the model.
Good luck

Looking at getting one myself