And he scored the winner against fallen giants Nottingham Forest on Saturday, which saw the Bees edge above the Iron at the top of the table.
Allen said: "I'm delighted for the people who have come together to pay Darren's wages for the five months he will be with us. I hope they are very happy.
"Our supporters' group 'Lifeline Society' came up with the money just 48 hours before the deadline and I was delighted to be able to bring him here.
"What's more, he wanted to come. There were other offers on the table but he wanted to come to us, once he is fully fit for League football you'll see the best of him."