Postcode distance checker

Hi all,

I need to look up 40k postcodes against a list of 22 postcodes to see which of the 22 is the nearest to each of the 40k.

I am thinking i would need to do this offline as there would be nearly 900k look ups.

I have a list of all the longitude and latitude of each postcode but I am not sure how I would actually do this in excel??

Any ideas would be GREATLY appreciated

Thanks in advance,

Kerry