London postcode Regex Validation
<p>I'm using the following Regex Syntax to validate a UK postcode in RSForm!Pro:</p>

<blockquote>
  <p>^(([gG][iI][rR] {0,}0[aA]{2})|((([a-pr-uwyzA-PR-UWYZ][a-hk-yA-HK-Y]?[0-9][0-9]?)|(([a-pr-uwyzA-PR-UWYZ][0-9][a-hjkstuwA-HJKSTUW])|([a-pr-uwyzA-PR-UWYZ][a-hk-yA-HK-Y][0-9][abehmnprv-yABEHMNPRV-Y]))) {0,}[0-9][abd-hjlnp-uw-zABD-HJLNP-UW-Z]{2}))$</p>
</blockquote>

<p>the validation works fine but i need to allow only Postcodes inside London.</p>

<p>Here are the postcodes allowed:
WC, EC, E1-E20, N1-N22, NW1-NW11, SE1-SE28, SW1-SW20, W1-14, HA0-9, EN1-8</p>

<p>Is there any Regex that validate only London postcodes and if not how can i run a separate validation after this and check the postcode is one of above.</p>