1. The structure of incentives doesn't encourage productivity. In other words, there is little incentive for colleagues to be active, deliver ahead of deadlines, propose new ideas, take on further responsibility, or outperform expectations. These things aren't frowned upon - of course - but there is no reward for such behaviour.
2. The organisation lacks rigorous tools to identify productive performance. In other words, a colleague who was assigned little workload could spend the first hour of the day completing her tasks (in a high standard), but devote the remainder of her day to watching kittens on Facebook and still receive great reviews in performance appraisals. A selected amount of colleagues thus choose to spend their days like this. It is still the exception rather than the norm though, thanks to the overall high calibre of staff.
3. Decision making is slow, and much of the work isn't really necessary for anything (despite the high standard of it, as mentioned above). In other words, if tomorrow the organisation would lay-off half its workforce, it would likely make very little difference to consumers and the communications industry. On second thought, it will probably benefit consumers; Ofcom would be reaching the same results but in a more concise manner and in a shorter time.
4. Pay is lower than in industry, and promotion is slow.