New Anglian mechanism (left). Old, discontinued version (right).
If you have old Anglian doors windows that can’t be opened the mechanism has probably broken. This can happen due to wear and tear, shifting in the building, or poor installation when new.
Even jammed or broken windows can be opened. The older mechanism types are long since discontinued but the later version mechanism can be made to fit with a few tweaks.
How long the newer gearboxes will be available for is uncertain.
Whatever make windows or doors you have, they can normally be repaired or improved. That is significantly cheaper than getting new ones installed.