In that case isn't the relevant question whether changing the policy would generate enough additional economic activity and tax revenue to justify the cost. To establish that would need data (or at least credible estimates) on things like: Whether that promotion that someone turned down was simply taken by another person without children in the appropriate age range, (or who is prepared to take a longer term view about their career despite the short term financial hit), who then is paid more so pays more tax. The cost of extending childcare support to affected families. Any additional income tax and National Insurance generated by increased earnings or hours worked. The extent to which people actually change their working behaviour because of the threshold. The cost of providing the additional childcare, including the effects on demand and availability.

Aw gawd....cue another 6 pages of discussion on camp stoves and BSS 😅