At vast expense, this week we have constructed our very own Wormwood Scraps Prison. The challenge facing the teams is to build tunnel-boring machines (TBMs) to break out and into the Scrapheap final.There are two walls, the second tougher than the first. The teams have to drill right through both, making holes large enough for every member of the team to fit through. The winner is the first team to make it through both tunnels.