This will replace your existing 1¼" McAlpine bend on your pan connector to take you to 1½" waste pipe.
https://www.wolseley.co.uk/product/mcalpine-t5m-a-95deg-bend-multifit-x-bsp-nut-15/
https://www.wolseley.co.uk/product/mcalpine-t5m-a-95deg-bend-multifit-x-bsp-nut-15/