Thanks God no-one is using this for important stuff like Policing... Oh hang on...
Police in England and Wales decided to move to Office 365 almost wholesale a couple of years ago, and whilst informed at the time about why this was a really bad idea in terms of individual and collective Force resilience, chose to ignore that in pursuit of getting everyone on the cloud.
In the past systems may not have been from a single over-arching supplier and that probably did make data sharing harder (though not as hard as is claimed - the systems to securely and safely share data absolutely existed, as did a closed secure and UK sovereign networking capability - now also pretty much close to abandonment in order to pursue 'Cloud').
What you did however have was inter-force mutual aid - which meant if a single Force's systems went down they cold easily rely on their neighbours to take up the slack.
Now that nearly every Force is moving to public cloud M365 (a move without any global precedent, and almost certainly breaking multiple UK laws in the process), when one is down all are down and hence mutual aid fails.
How is this progress?