UK Postcode

I have a list of UK Postcode that I need to check for the correct format.  

Users address are entered like: $address = "street, town, city, county, postcode";

I split these up into parts like so: $part = explode(',',$Address); which gives me:

$part[0] = 'street';
$part[1] = 'town';
$part[2] = 'city';
$part[3] = 'county';
$part[4] = 'postcode';

But some users enter their phone number instead of the postcode which gives me a pain in the head...

So i'd like to check the last part in the string so I can either put the value in a $telephone = '0123456789'; or $part[4] = 'AB10 1LB';

So how would i check the format of a Postcode? example: AB10 1LB

thank you