The parent company, CGI, is massive and is as bureaucratic and resistant to change as all such big institutions are. They force a large amount of unnecessary (online) paperwork onto the Glasgow office, online training, internal CVs and skill matrices, etc. You can lose hours just trying to fulfil the latest barmy request and you'll never need any of it. Also as many of their customers are government agencies the amount of paperwork you may be required to do for a security clearance to start on a new project can be insane.
Overtime is a rare thing (usually only at the end of a project) and is usually (but not automatically) paid, but you often don't get much notice (sometimes you find out the same day that you're expected to work overtime that evening). This is not common and there's usually some kind of compensation for it above the merely financial (e.g. WFH for a week instead of your normal 2 days) so it's by no means a major negative to working there.
The Glasgow office is a massively open-plan layout, with typically over a hundred people in the office at any given time, so noise levels can be an issue. If you're on the autistic spectrum at all and open plan can make you uncomfortable, then this won't be a good working environment for you (it's *extremely* open plan). Also the Glasgow office is run by an extrovert who likes to find spurious reasons to have meetings, demonstrations, etc and likes his employees to do the same. If you have an introverted personality type you will feel at a disadvantage compared to your more extroverted counterparts when working here. The management are all good people, though, and you *can* talk to them about any issues you have.