It strikes me that the more they merge IT departments across forces, councils, etc, and the more they centralise purchasing, then the more they ARE repeating the mistakes of the past.
By definition, centralised purchasing is slower, unreactive, and away from the frontline - and much as it has the power to negotiate 'better' deals, there are also a limited number of companies that can bid for the megadeals.
i.e. a single UK wide deal with Tata Consulting might be cheaper than employing local IT service firms, but I'd question whether the level of service is competitive - from what I can observe as an outsider, it is considerably worse than would be accepted in SMEs, who would quickly change provider if they were being mucked about with - because they don't have to go through a huge bidding process to do so.
The same is also true with software - the more they centralise and standardise, the less competitors can be sustained by the market, which means less competition.