I have already upgraded the forks when I got the bike and have been thinking of upgrading the rear shock which is Fox float R and wonder if it is worth doing and if so what to. I mostly ride in Kent and North/South Downs.

rp2 is all you need for maestro

Get it Pushed instead, it's probably cheaper than upgrading and will give a much better performance than swapping for a shock with propedal switch.

I got the Float R on my Trance 3 Pushed and was amazed at the improvement. It was more taut, more supple, more controlled and generally just lets me ride faster.