Water ingress through brick wall.

Hi Nick

A few points

1. The wall on the right-hand side of the image (directly above the last weep hole) looks particularly wet. Is the guttering leaking in any capacity?
2. The weep holes appear to be fitted on top of a 10mm bed, these really should be as flat as possible on the cavity tray. It could be that you have a 10mm pool of water sitting at the back of the cavity tray and cannot escape because the weep holes are 10mm too high. Although the cavity tray should cope, it's still not good to have water pooling.
3. The lead flashing should really have been a continuation of the cavity tray, and started from the same course.
4. There looks to be some cracks and gaps around the window seal directly above. Make sure these are repointed to prevent water entering the cavity.

Along with the above, I would suggest removing the inner plasterboard and exposing the steels and cavity for further exploration. The plasterboard is going to need to come down anyway.

I hope this helps.

David