If it is a new costume, the trousers are reminiscent of Patrick Troughton's costume from the late 1960's. A throwback to an earlier era of Who, perhaps?
NEW 12TH DOCTOR COSTUME! 😎
navy coat & hoodie
black holey jumper
plaid trousers
Dr Martens shoes
#DWSR
💥💥 pic.twitter.com/8hmd7Va36M
— amber lamba ⭐️ (@amberlabamba_) March 31, 2015
[Source: Twitter, DoctorWhoTV]