Studio Bark gifted the cutting patterns – and told Dezeen that some of its employees are part of Extinction Rebellion (XR) – but the practice itself was not involved in delivering the project.
"It's a natural extension of what U-Build was meant for," Nick Newman, a director at Studio Bark and member of XR, told Dezeen.
"This is about what a group of people all coming together have managed to achieve. You can call it protest architecture, or architecture of activism. It's a new typology."
U-Build's modules were re-designed to be simple enough that complete novices could build them, with just one shape of box and an easier bolt system.
Pieces were cut at a community-run CNC workshop and supplies were bought through crowdfunding.
Circles were cut into the sides of the boxes, allowing activists to lock on through them – a peaceful protest tactic where people attach themselves to shut a site down. Locking on through a structure makes it harder for the police to remove protesters.
Each plywood box weighs just five kilos and has two handles cut into the sides, so XR activists can carry several boxes at a time and quickly assemble them into a pre-agreed structure.
A tower made from the boxes in Trafalgar Square this week had three XR protestors locked onto it, and required the police to bring in heavy machinery to take it apart.
Newman was one of the people locked on to the modular tower, and he was subsequently arrested.
"It's one of the best things that I've done in my life," he told Dezeen.
"To be able to see U-Build – something we always envisaged as a kind of community asset, a way of people making their own structures – in a different way. To be able to witness that was really quite special."
The University of East London, where some of Studio Bark are tutors, did a project looking at the multitude of ways the boxes could be arranged and bolted together.
Along with the tower, the boxes have been used to create stages for activists to deliver speeches from, and benches for visitors to the protests to rest on.
XR, which has been banned from protesting in London by the Metropolitan Police, is currently crowd-funding to build more boxes for future actions.
The group previously disrupted London Fashion Week with a funeral procession, calling on designers to find a way to be creative without "creating more stuff".
U-Build is a modular construction system designed by Studio Bark to allow people and communities to self-build structures. A flat-pack kit of parts allows users to build modules that can be slotted together with hand tools to form houses or extensions.
Photography by Joe Giddings and Andrew Whatty.