The quickest way to get it - would be to telephone NatWest customer helpline, and ask someone !
The address for the Hilton Cobham is Seven Hills Road South, Cobham KT11 1EW, United Kingdom. Instructions to get there are found on their website online.
London has thousands of different Post Codes. Each group of around 10 addresses has its own code and some large buildings have their own code. A London post code would look something like this: SE25 2TP or E16 5LS.