Switch from Civil to Mechanical/Aerospace (University of Manchester)

I have received an offer through clearing from the University of Manchester for Civil Engineering (MEng H201).
However, I would prefer to do Mechanical or Aerospace Engineering.
Is it possible to switch from Civil to (Mechanical or Aerospace) within the first 3 years?
If not; is it possible to finish a BEng in Civil Engineering and then take an additional year of (Mechanical or Aerospace) to receive a Masters.
I understand that Civil shares a few modules with Mechanical and little with Aerospace so I am prepared to stick out the 4 years in Civil if no switch is possible.