Someone is suffering from memory loss, as Luton was refused permission to expand by the government, which is why the famous marquees were put up. In fact Luton was meant to shut down with the opening of London’s third airport so someone buying a home in the 70’s could have expected the airport to eventually close. From the mid 70’s until the mid 90’s the airport stagnated with passenger figures usually well below 2m, as passengers and airlines headed for Gatwick, so it was reasonable to expect this would continue. Different story from the late 90’s when by this time the airport was taking off but still it was claimed the new terminal had a capacity of 5m when it opened in 1999.
Watching the video (sound track starts after a few seconds) the only thing to change is that it is now airport policy to pack out the terminal while in 1974 they were apologising for the overcrowding while blaming the government.