[JonnyA]

A few months on and thought that i should update this in case it helps anyone else out.
charging the battery up seemed to make no difference. Charger took it up to 12.7V but this dropped back to 12.3v after about 24hrs with the car stood unused or used for the usual 40min commute work day.
Bit the bullet and took it into the dealers with a full written description of the issues and also spoke to the workshop tech. Their opinion;
1, battery voltage slightly low (but the in car system is not reporting this as a problem, despite it being 'very sophisticated') so give it a good charging since (as Clan said) the car will only take it to 80% but the start/stop will not operate if charge is below 80% - how does that work in the real world???
2, starter motor is sticking - hence random failure to start - and recommend replacement - at about £450.00 I know they only had the car for a couple of hours and in this time it behaved itself but i am pretty convinced from recent experience on my other vehicles that this is not the issue.
Credit to the dealer, they did not charge me for the diagnostic time.

My actions - replace the battery. This seems (touch wood) to have sorted out the issues with start/stop, the random non-starting and a couple of other minor changes in 'behaviour'.