In the 60s and early 70s there was legislation which was called 'the wage stop'.
This restricted National Assistance payments to what wages were locally.
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Poor Parents: Social Policy and the ... - Google Book Search
I was never called on to administer it but recall the comments of work colleagues who did.
The weekly benefit was restricted to match the wage of a council labourer.
It mainly affected large families where the additions for several children caused the assistance rate to get quite large.
The effect was to put those children in poverty conditions and that is why it was abolished.