As a Manc i might be biased in saying Manchester really isn't as dangerous as everyone makes it out to be. I was walking and taking the bus to and fro school, from age 11 to 14 sometimes in pitch darkness in winter, without any issues whatsoever. As long as you stay clear of the 'dodgy' areas, (you'll have no need to go there anyway) then you'll be as safe as you would be anywhere else in England.