I would not call the STER commercials commercial radio, Paul.
Certainly it was n't independent radio.

The UK had commercial TV (ITV) as from 1956, so the step to comm radio was a bit easier.

In Holland politics and the public broadcasting system is very tied, so indepentent rtv was blocked for a long time and came when Eurpean laws enabled it.
Radio on airwaves didnt come untill the late 90-ies when the European rule was applied that ALL channels not used by a public broadcaster MUST be put available for commercial radio. Many countries neglect this rule.