 SPOILER: At the end of the film, the airport building plan is  switched from Alis home in Staines to Slough, another town nearby.  Both towns have a dismal reputation in the UK (as a policeman says  to Ali, "Staines is shit hole." See also poem by John Betjeman:  "Come friendly bombs and fall on Slough"). So it is a natural joke  for UK viewers.