Interesting topic. Some may find this web page interesting from the British Army Rumor Service (ARRSE) concerning what is a WALT:

http://www.arrse.co.uk/wiki/Walts

The bottom of the page has several examples under "well worth a look"

It is sad to read about some famous outed walts such as:
The Baron of Castleshort (nice kilt pics)

http://www.arrse.co.uk/wiki/The_Baron_of_Castleshort

Of course these are the most extreme examples of pretenders.