Leak in cavity wall

My advice on this would be to eliminate between roof and walls as to where the water is coming from. simply get a hosepipe and soak the wall above the window by replicating driving rain on your brickwork. if this has the effect of producing water as you have said coming thru the window then you can discount the roof and prove its coming thru the brickwork. So if this is the case repointing is needed undertaken by a builder who should cut the mortar out to at least 13mm b4 repointing. When brickies built houses a lot did not fully butter their cross joints this is usually the point of ingress of driving rain. I have actually taken down internal walls to prove this point ,you could actually see daylight thru the outside skin of the brickwork, it only takes an hairline crack in mortar joints to cause capillary action of water being sucked in thru bad brickwork. hope you get sorted!

It’s likely their is a fault in your roof somewhere , water can get in anywhere and travel down and up with capillary action. along the wall I would imagine it’s something to do with the flashings or could be higher up along the ridge a professional should be able to help you. We hope this helps

could potentially be a build up of mortar in the cavity tray that is installed above the window opening over the lintel, or could be the dpc that goes over the parapet walls is not correct and water is trickling down , take videos when it happens next and really is something that can only be looked at to identify what it is .

Brickwork at side of house may want repointing and sounds like you need a new cavity tray install above office window

You could have a blocked cavitiy wall but you would have to open up the cavitity wall to see also you could have a horizontal or vertical dpc issue above or around the window and no weep vents this would cause the water getting in around the window

Needs repointing and weather sealing

Wall ties not properly cleaned And maybe repointing needed