I have now had my car back from the dealer.
The dealer wanted it for one day but I persuaded them to keep it for two days as I didn't want to miss any of my work related activities.
So they agreed - In the end it took them 2.5 days.
The work carries out was as so:-
Reprogram the ECU memory
Remove cam head cover
Adjust valve clearances
Replace two gaskets (as they don't reuse gaskets - I did spot the price of one gasket as ~70GBP+VAT)
Thats all that was done and it took 2.5 days.
I seemed to have lost all my radio station presets and my MPG data (I hadn't reset the trip computer)
I should now see if there is any difference over the coming weeks.