I amtrying to remove the wiper arms on the Mk 4 astra it does not appear to have the platic cap and the nut on the spindle as in previous versions and I cannot see any other release mechanism do I need a special tool or something?

Thanks

Probably has a hinged cover on the bottom of the arm with the nut under the cover, it also helps if you have a small puller as the arm can be tight on the spindle

No that was how the Mk3 was th mk4 has a flat metal pressing for the arm with what looks like a metal cylinder stamped into it this I have tried to twist pull and dive off with a wedge without any sucess