The piece looks way too short to be a flaperon from a B777. From the second photo in Telegraph article, it's at most 2.5 m long. B777's inboard flap is at least 5 m long. Either it got snapped in half (doubtful, since both edges look straight), or it's not from a 777.
Yemenia's Airbus 310 flap would be closer in terms of dimensions.