The 21-year old midfielder departed Tannadice for The Hawthorns in January 2012 which was a move which ex-manager Houston described as 'greedy'.
Allan admitted he had a tough time when pondering the offer from Albion and said Houston's behaviour eventually forced him out.
"I wanted to stay at Dundee United. I always thought I was going to sign there," he told SunSport.
"But because of circumstances with Peter Houston that wasn't the case. He tried to belittle me in front of the other boys. He publicly criticised me for being greedy when he knew I wasn't.
"He wanted to put me under massive pressure.
"I didn't want this money or that money, I just wanted a decent contract and to get playing again for Dundee United.
"The way I was treated made up my mind. If there had been a middle ground with United none of this would have happened.
"I didn't appreciate what he did to me and that's why I decided not to sign. I remember going into a meeting with my agents at the start telling them I wanted to stay. Then I went to training and was treated like an idiot."