He said: "I think it's fair to say the performance was not up to the standard required.
"I made my feelings clear to the players, friendly or not - only the very best will do."
The Bees host the Iron at Griffin Park on Saturday, the first of three games in quick succession - and Allen is desperate for a good start.
He added: "There must be significant improvement in the week ahead, when we play three games in nine days.
"It is imperative that we get off to a good start."