Mugsy,
I also have a Mk1 and am planning to do this.
The current cost for Roksan to upgrade the CD player is £345. For this they will upgrade the CD player to latest M series spec, the model that superceded the Mk2. They don't replace the face plate, so it will still look like your Mk1, but sonically will perform like a M series which currently cost £1100.
FYI, if you have other Roksan components, it might be worth you joining their cognesciti club. It costs £100 to join, but for this you can get your Roksan kit serviced for nothing, and 20% discount on parts and upgrades.
So the cost of the CD upgrade would be £276 plus £100 joning fee. So you will end up paying £376 for the upgrade and club membership - an extra £31 and for this you can get your amp serviced for free.
I tried to book my CD player in recently, but factory is closed for a fortnight.
See
http://www.roksan.co.uk for full details of upgrade and the cog club.
Hope this helps