Yeah, on the bridge sequence you could see a few Union flags in the background (out of focus) but most other things covered well (including reg plates, many blurred as they would have give it away) to make it look like England.From Wiki.
Series one was filmed in Birmingham (including pub interiors in the Queens Arms)[10] and series two and three in Belfast by BBC Northern Ireland, per the end credits, though the city is not identified in the script in either series - set dressings and props indicate that the unnamed city is Birmingham (maps of Birmingham appear on walls, and telephone numbers use the 0121 area code ). A photo gallery of exterior scenes from series two shows the 4th Street Station on Ormeau Avenue in Belfast