There wasn't any coursework - just a single thesis at the end. I think some people do achieve a PhD alongside work, but it can be a long process. I also think things have changed these days in that decades ago you could take as long as you liked, whereas now they're very strict about you handing it in completed in 4 years after registration. It maybe that you can register part-time and the deadline is subsequently pushed back, but I imagine it can be a bit risky as departments change and supervisors will come and go if you're taking more than 5 years to do it. The other aspect is what type of PhD it is. For laboratory work it can be hard to fit that around work, especially if you're receiving samples on another timetable.