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Mine were dispatched recorded delivery on about the 12th April, I was away for the week and upon my return there was a little card through the door telling me to pick up my letter from Haywards Heath sorting office. I went into the "customer services" office and the first thing I saw was a brass plaque on the wall. It commemorated a man called David "Dixie" Dean 1937 -2001, underneath it bore the legend "I know its (sic) here somewhere". Whilst Dean was a fine footballer, the master of the dribble, he evidently didn't know much about the postal system.
In short, I think you can safely assume your tickets are "lost" and I would contact the ACO accordingly. I would not recommend gunning down your postie though. Unless they have changed policy in their efforts to "manage down" staff numbers, the GPO take a dim view and will generally prosecute customers who abuse, threaten or murder Post Office employees. You could face a hefty fine.
BTW I hear the Surrey Post Office Sports and Social Club are doing LM this year....