Hi all, just so you know what happened with this, I got another roofer to do the work in the end, and he said the verge cap was just a design choice, it didn't have much of a functional purpose but it didn't hinder anything either. He took it off and found exposed brickwork (about an inch) running up the verge of the roof. The rain must have been coming at the house from a specific direction and being blown sideways at high speed for a long period to get enough water on the exposed brickwork to soak my bedroom wall. He slotted in a lead soaker and refitted the verge cap and I haven't had a problem since. See attached for lead soaker work.