I promised you more soon so here it is.
Having undercoated the M20 in Halfords automotive grey primer, which in my haste, i forgot to photograph. I then proceeded to put on the first coat of olive drab. For this i used vallejo model air olive drab No.71043. I will use this as the base colour and lighten, darken the colour appropriately.
There has been a lot written in books and online about Olive Drab and what constitutes the correct shade and which brand of paint is the most accurate but in my opinion it's up to the person painting. If it looks right to you then that's all that matters. I like Vallejo air as it's pre thinned and i like Tamiya as well. I use both to give a slight variation in colour.
Here is a couple of shots of the base colour on. I had previously sprayed the wheels in black. Olive drab has been sprayed onto the hubs and i will now proceed with the detail painting of the wheels. fitting will take place at the final stages and then the guards will be added. This way i can give the wheels my full attention and try and get the look i'm aiming for.

Olive drab first coat.

The masking doing it's job!