If you think of that wall,” says Dave Jones, gesturing at a particularly grim section of Victorian institutional architecture, “that’s what the whole place used to look like: brown and grey and, on a day like today” – the weather is standard-issue English overcast – “not very inviting. But just by the inclusion of flowers it makes it feel different.”

And so it does: the blooms tucked into apparently every available space, in hanging baskets, pots secreted in spare corners, raised beds flanking imposing gates and doors and long plots dug into the ground, only seem brighter – sometimes almost glaringly so – against the soaring fences, razor wire and ubiquitous steel bars.