This article examines the dynamics of the maintenance of illegitimate children in London during the protracted ‘crisis’ of the old poor law between the 1790s and the 1830s. This was a period of rapidly rising illegitimacy as well as national, and metropolitan, poor law expenditure. The affiliation system offered parish officials a parallel system by which poor rates could be deflated, but analysis of the 1834 Town Queries reveals that metropolitan parishes could be particularly poor at recovering the costs of chargeable bastards from putative fathers. The article interrogates in detail the workings of the affiliation system in Southwark and Lambeth in terms of the proportion of fathers (and mothers) who paid maintenance for their children, either in lump sums or in weekly allowances, plus the associated costs of childbirth and legal fees, the range of weekly sums, which could be higher than previously thought, and the duration for which they were paid, which could be surprisingly long. The article reveals a complex system, variable at the parochial and regional level, as was the wider old poor law.