There can't be many businesses in the UK that are both that big and that spread around - the BBC has offices in most major cities, no purely commercial business would operate like that because they don't need to. Maybe the big retailers like M&S have a similar amount of staff in a similar number of distinct locations but their business operations don't require as many individual items of IT kit, at least not kit that's easily nickable for resale. Various reports suggest most government departments lose/have stolen etc roughly 100-200 laptops/tablets per year, so 600 in five years is actually towards the low end.
You could ask now many 'the NHS' loses, but in reality the NHS probably doesn't really exist in those terms any more. You'd have to ask each CCCG individually and then total the figures up.