I decided to separate my pregnant platy's into a breeding hatch as they refused to give birth, being chased around by males may have had something to do with it!
Don't know if anyone is interested how I got on.
On 5th August

One of my female platy's give birth to about 30 fish, OH MY GOD panic!
A local fish shop has agreed to take them, when they are big enough to not get eaten.
Following that only 6 survived and are now doing very well.

I have since put them into the main tank using a tank divider, which has tiny holes to allow the air to flow. The other day I noticed that I had some new babies, surprisingly on the divider side, it appears they have squeezed through the air holes.

I am now the proud owner of 10 new ones, we will see how it goes.