It's a nice place to coast and retire, but not a good place to thrive. There isn't really a "culture", it's more a building full of individuals working alone. Colleagues certainly aren't openly hostile, but there's a pervading attitude of gloom and regressiveness.
Success is defined as invoking process, obstructing change and scoffing at new ideas. It's a very wasteful and bureaucratic environment. A project is usually a whole floor of middle managers sending powerpoints back and forth, with one stressed-out grad in the corner on Matlab doing all the real work.
The outcome is overspent and delayed projects, whilst the project team pat themselves on the back for following process.
A lot of people are complimentary of the work/life balance and pension but I don't get it. WFH isn't a serious option and there aren't really other benefits apart from free instant coffee, and the pension is generous in % terms but ends up lagging in £ terms due to low salaries.