Been looking and looking and looking and from what I can see I would need to update the CAN, the prices seem to be around £75 plus so all in all might be better off getting an aftermarket OEM looking item from Fleabay! - I'll get Sat Nav and other functions (might even go for an Android one and use Torque app etc) and be able to use the MFSW still..
Unless there is an RCD310 firmware update that retains the original CAN but stops the battery drain - I can't find this info out yet though!
I would prefer all OEM but don't mind tbh.
I'll continue to search.