It is, of course, a backstage pass. The boys entertained themselves (and us) all weekend with the preparations for a concert to be given by themselves to a select audience (Nigel and I). They selected their costumes (sunglasses and baseball hats), practised lip-synching to their playlist (High School Musical and The Backyardigans), and issued numbered tickets, as well as the treasured passes.
Possession of the pass entitled the bearer to go and sit on the bottom bunk along with "the band".
* While googling the correct spelling of Locarno I found this: http://theundertones.net/ugigs.htm a list of all the Undertones gigs. I think I met Feargal during the 1980 tour as it was not the first time I had seen them and I think I saw all their appearances in Portsmouth!