Universal Credit minimum income floor: apply reg 62(1)(b), the couple rule and net thresholds

[MaxGhenis]

The UC minimum income floor (policyengine_uk/variables/gov/dwp/universal_credit/income/income_floor/) differs from UC Regs 2013 reg 62 (https://www.legislation.gov.uk/uksi/2013/376/regulation/62) in three ways.

1. Who the floor applies to (reg 62(1)(b)). The floor applies only to a claimant who "would, apart from this regulation or regulation 90, fall within section 22 of the Act (claimants subject to all work-related requirements)". The model has no work-related requirements group, so it also floors claimants who are exempt: those with LCWRA, carers, and lone parents of young children (Welfare Reform Act 2012 ss.19-21; UC Regs regs 89-91; ADM H4061).
2. Couples (reg 62(3)). For a member of a couple, the floor applies only when the claimant's earned income is below their individual threshold and the couple's combined earned income is below the couple threshold. The claimant is then treated as having min(individual threshold, couple threshold − partner's earned income). The model uses max(own earnings, floor).
3. Net thresholds (reg 62(4)). The thresholds are the reg 90 amounts converted to net by deducting income tax and NICs as the Secretary of State considers appropriate. Earned income is also net of the reg 55/57 deductions. The model compares a gross floor with gross earnings.

Both routes into the floor are affected: self-employment, and owner-managers treated as gainfully self-employed under reg 77(3)(c) (#1965).

Raised during #1948 / #1965.