Ive worked in the catering and hospitallity trade for some time and as far as i understand it all persons handling food and beverages should hold a current Basic food hygene certificate, however some leeway is given to "new staters" if they havent taken the course but are signed on to it and are working with someone who holds one.
I would imagine that if the promotion is for one day only, your husband should be ok if he is with someone who has the certificate.
There are many people out there who work with food that dont have the qualification and are still working and questions dont get asked and if they do its the employer who is liable not the employee. However, in the uk, you should have the certificate before serving, preparing or distributing food to a customer.
AMMENDMENT
http://www.cip.ukcentre.com/food1x.htm
This site is the full General food hygiene regulations 1995
The regulation say that you must adhere to the regulations and interestingly that although a certificate is prefered it is not mandatory.
It takes you through the basics of food hygiene and the lagal requirements of HACCAP.
But basically your husband can rest easily, he shouldnt have to take the course as long as he conplies and remembers to wash his hands.
(sorry about the first bit, that was always what i believed to be the case)