You can buy the formulation that was invented in 1923 for cheap.

It's newer formulations that are expensive, and those are still protected by patents.

Insulin is a great example of abuse of the patent system. The original patents for all of the major modern insulin formulations expired years ago, but the manufactures filed new patents years and even decades after the products had already been on the market to extend patent protection from 20 years to 30+.

The NHS pays £14 - £28 a vial for those newer formulations.

Good for them. Maybe if we fixed the patent system (government enforced monopoly) we'd be in a similar position.

The UK has a patent system.

That just raises more questions. Are these "newer formulations" a meaningful improvement over everything else (in particular those for which patents have expired) created during the past 97 years, as opposed to ploys to maintain IP? The tactic involved here is using regulatory capture, near monopoly control of supply and IP law to limit what is available for prescription use to expensive products.

Mostly, yes. The newer insulins (well they've been around for 20 years) have molecules which are engineered be faster acting so that they reduce peaks in blood sugar after meals; or longer lasting, so they can provide a more predictable background coverage.

Not the same insulin.