I have an old 60 year old house that has a raised timber ground floor
above a concrete floor. The void is aprox 3 ft.

Traditionally you would fill this with hardcore and then a layer of
concrete, to form a new floor.

But my wife insisted on getting laminate flooring ontop of the T&G and
beams, and I do not want to lift that.

Is there any other way of insulating the floor void. I have thought
about injecting cavity wall insulation.

Any ideas or suggestions that the regulations people would accept ???