Queues are a result of mentioned instruments. Say a hospital has a CT scanner capable of 10 scans per day, 3,5k scans per year. NHS pays for 500. A hospital can fully utilise the scanner and blow their yearly budget of publicly funded scans in two monts, do 10 free scans a week or do 8 scans and save 2 for emergencies. Placing more scanners does not reduce queues.
The CT scanner is usually owned by the NHS trust, which makes the marginal cost of using it rather small. It's almost the other way round: having bought a big capital asset, the incentive is to make sure it's kept busy being used effectively. The NHS "internal market" obfuscates this hugely, but there is still no incentive to over-provision because the system can't drive up external insurance costs.
