Right word, wrong form, # 1

This mangle comes from an email sent by the Civil Service Motoring Association (CSMA):

Collins English Dictionary is unambiguous about the correct form of the past participle of whet:

Link: Collins English Dictionary, ‘whetted’

The entry for ‘whet’ in the online Oxford Dictionaries is identical for British and US usage:

Link: Oxford Dictionaries, US English Dictionary, ‘whet’; British & World English Dictionary, ‘whet’