The best (and complete) solution is to install the "English (United Kingdom)" language pack.
This can be found by going to: Control Panel [make sure you select 'view by: Small icons' in the top right so you can see all items] then select 'Language'. Here you will see the default "English (United States)" option with "enabled" against it and should see the "English (United Kingdom)" option below. [If not you should be able to find it via the 'add a language' button] Click on options and then the "Download and install language pack button"
Just wait for it to install then highlight the recently installed option and click the 'move up' button so that this becomes your default. It should display "Will be enabled on next sign-in". It will do exactly that, after a reset it will be enabled and should be your default.
This will then give you the wider variety of date options i.e. dd/MM/yy and d/M/yy that (as mentioned above) is not an option otherwise.
Hope this helps