I suggest that if you really want to fill the cavity then you use polystyrene beads.

Most likely it is a solid wall though

Generally only properties built after the 1920s would have cavity walls. You can check the brickwork, compare it to the picture shown on the bottom of this page:
 
http://www.government-grants.co.uk/cavity-wall-insulation-grants.shtml

I have a 1930's semi house built in engineering block i.e a 9inch x 9inch x 18 inch concrete block with two number vertical squares 4inches square.
Does anyone have experience of cavity filling either by injection or gravity from the top in the roof space.
 
At present the voids are sealed at wallplate level but could easily be opened .
 
Any suggestions?

they will be difficult to fill from the top as not all the voids will be accessible and the presumed polystyrene beads will clog up and settle later.
 
If it were mine I would do it anyway -- probably on a diy injection basis = lots of holes.

I did this once using perlite as these are heavier than polystyrene. However you really need to be able to see down the cavity to do a proper job. the holes never really line up so as tony say, it will be difficult. Consider an internal insulation (external will not work very well due to venting of the blocks).

Attempting to insulate brick or stone built houses is not easy, and the amount of insulation that could be "injected" into the cavity would not result in any noticeable bettering. Our houses in Sweden have floor and wall insulation of at least 200mm, and roof insulation up to 500mm, which together with triple glazing ensures good protection against not only the cold, but also the warmth of the summers, and noise reduction.

There is a rerason why cavitie walls where build.
Does this reason still exist? If yes then keep the cavity for it's purpose.
Some buildings can't be cured.

Sounds like a solid wall to me. You could consider external wall insulation which would help keep the heat in the house and the weather out. Look at www.energymortgage.co.uk for info, they can arrange surveys etc if you wish