The changes follow the introduction at Spa of an upgraded Honda power unit. They mean Alonso and Button are now on to their seventh engine of the season, two more than the regulations permit for new engine manufacturers.
Both drivers have also taken on new turbochargers, MGU-H and MGU-K, all in excess of the number allowed by the rules, and Alonso has in addition used a new Control Electronics component. The resulting, multiple grid penalties - a 30-place drop in total for Alonso, and 25 for Button - mean they are certain to fall to the back of the starting order.
With untaken grid drops no longer converted into in-race penalties following the recent rule change, it raises the likelihood of McLaren taking the opportunity to use a further, eighth engine on both cars on Saturday. Such a change would incur further penalties, but these would have little or no impact on the team's starting positions for Sunday's race.
More importantly it would make two upgraded engines available to them for each car for the season’s remaining rounds, without the risk of further engine change penalties.