If no-notice inspections are to be undertaken I would suggest - with my tongue only partly in cheek - that the same principle should apply to inspectors as to schools.
Inspectors would get notice of the school to be inspected by a text message early on the day of inspection. With no prior test data, they would have to visit the school to inspect what they found on the basis of what they saw in classrooms rather than pre-conceived ideas, data analysis or discussions in the head's office. Inspectors and schools might be surprised, even gratified, by the findings and a degree of trust might be restored to the inspection process.
Professor Colin Richards, Former senior HMI, Spark Bridge, Cumbria.