Potential Cause for these Bay Window Cracks in Victorian House in London
The cracks are caused by settlement, evident by the separation of the window sill and the wall. I suspect the settlement is caused by water. What you can do is 1) repair the concrete walkway and apply the flexible sealant to the concrete-wall joint, and 2) grade the ground, or correct the slope of the concrete walkway, to allow water to flow away from the building, also the downspout, if any.
After the corrective actions, patch the wall and monitor the situation. If the cracks reappear soon afterward, then you might need to contact a structural/geotechnical engineer to check/work on the foundation.