Disclaimer! I have only worked for booths so my experience is pretty limited when it comes to other employers.
I currently hold the title of Duty manager(not dept manager). Booths has recently undergone a management structure change(end of 2015) and so is struggling to cope with re-organising itself in a new format. How it is currently running is, Dep manager are now responsible for doing 2 or even 3 of the jobs that the old dep managers did. This puts them under immense pressure)especially if the store is large/not performing well, think 60hrs a week for less than 22k), this means that the supervisors and now on the whole running the departments, doing wages/holidays/rota's etc leading to a increase in errors and problems as no extra training or support has been offered, all for 16-17k. This has inevitable led to a talent drain from the company, with new management being brought in from M&S(on the whole).
Everyone is expected to do at least one midnight and one 6am start. A perfect booths employee looks like 18+, on a 8-20 hour contract, but expected to do 39 and willing to work hard! Frankly there is no incentive to work for Booths as they have done away with graduate scheme and do not offer anything above minimum wage less than a pound more for supervisors.
Although progress up to Duty manager is fairly easy, any further steps is a case of waiting for someone higher up to leave. Ultimately there is not great career opportunities at Booths and other retail operations offer better potential futures.