Postcode validation

[lydz]

hello all
this thing is really bugging me im trying to come up with a post code validation and i have tried dozens, which should have worked really, but just havent so wondering if you guys knew any
examples of postcodes would be

BN3 8JH
BN41 8JH

theyre the only two types that are bound to be entered really

the first and second characters have to be a letters
the 3rd has to be a number
the 4th is sometimes a letter (not always present)
then theres a space
then there has to be a number
letter
letter

any suggestive codes would be great, as none of mine have worked its in access

thanks
nightmare lol

 

[lydz]

sorted
using an input mask makes it so much easier
i am pretending they only come in one form, but i can live with that