At the start of the month, London mayor Sadiq Khan trumpeted a £3.46bn investment to build more than 29,000 affordable homes, part of a wider strategy to deliver a promised 79,000 cut-price homes across the capital between 2021 and 2026.

The selection of the partners to deliver the homes was eye-catching for a number of reasons. Most obvious, was the major role given to councils building the homes, but also interesting was a huge hike in grant rates, and the extent to which many of the usual suspect registered providers – the major London-based G15 housing associations – were taking a smaller role than previously.

But there was one particular detail which was initially impossible to explain.

This was: How could £3.46bn be the amount needed to build 29,456 affordable homes, given that the budget for the overall 79,000 homes promised in the next five years is – as was made clear here - just £4bn? In other words, with £3.46bn allocated to be spent on around 29,500 homes, this left just £540m for the remaining 50,000 affordable houses. It didn’t make sense.

As it turned out, the answer to this question tells you a huge amount about the state of affordable housing delivery in London over the next five years.

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