An easy answer HP19 8DE and HP19 8DP are served by cabinet 65 on Aylesbury exchange and it is NOT live.
Is it due to be live by the end of September 2015, see date at https://www.btwholesale.com/includes/adsl/main.html
Though suspect that this is a date that keeps shifting and there may be some issue in getting the cabinet into a live state.
shows cabinet 65 and looks like they were probably working on the copper interconnects on the day the Google car drove by.
So delays likely to be down to power or fibre linked back to the exchange
The other end of Gatehouse Close has a Virgin Media cabinet, but the postcodes don't show it as available, but with new expansion plans VM might be receptive to expanding into close OR at the least their business fibre services might be cheaper than BT Group Ethernet/leased lines.