Why do our windows leak?

Unfortunately Chris there's no modern easy fix that might not make the problem worse. If the water did not penetrate before the windows were fitted the cause of the dampness might be difficult to find. It's worth looking at which elements are new or different - should you have removed overhead lintels with drip grooves, external timber architraves or lime render, then the missing details could be reinstated. Next I'd check the mastic seal around the sides and top of the window and renew this if it's missing or uneven, use a long-lasting paintable kind such as polyurethane.

The cement mortar pointing above the openings won't help matters as cement shrinks slightly when it sets and can leave cracks which allow the water to get in. My suggestion would be to replace the adjacent cement mortar with a lime mortar made with either lime putty or hydraulic lime. This will hopefully return your home to it's dry state.