Most UK 'big city' centres are crime and drug ridden shitholes but Plymouth does seem to have far more than its fair share of problems. This is mainly because it's nearly all retail space much of it now unused and there is literally nothing else there. Plus the council homes a lot of its problems in and around the city centre. Walk through the city centre after about 17:00 on any evening and its mostly deserted apart from druggies and gangs of knobheads.