Luton have apologised to their fans after a number of Sunderland supporters watched Sunday's title-winning match from Kenilworth Road's home end.
The Hatters have been inundated with complaints from their supporters since it became apparent that many home tickets found their way to visiting fans keen to see their side claim the Coca-Cola Championship title.
But while the relegated club apologised "unreservedly" to Luton fans after the 5-0 loss, they insist they did not sell the tickets.
A club statement read: "The club can confirm that the ticket office only sold tickets to those supporters who were registered on its database.
"While we could not prevent Luton supporters from selling their tickets to Sunderland fans we could, and in hindsight should, have imposed a ban on anyone wearing away colours from entering all home support areas.
"The club apologises unreservedly to all Luton supporters."