Alonso had already been hit with a five place grid penalty after he was forced to take his fifth 'Control Electronics' of the season, drivers are allowed just four of each power unit component.
After a promising Friday, when Alonso was well in the top 10 in both First and Second Practice, Honda decided to try and optimise a good result in the next race, in Hungary, which should suit the McLaren-Honda MCL32 better than the high-speed nature to Silverstone.
He will take a sixth 'Internal Combustion Engine (ICE)' of the season, a sixth MGU-K, and an eighth turbocharger and MGU-H.
Slow but steady
In the last race, in Austria, Honda's new upgrade or 'Spec 3' of its power unit provided Alonso and team-mate Stoffel Vandoorne with the ability to be in mid-field and fight for position. Unluckily for Alonso, he was taken out at Turn 1.
While Vandoorne's car had no problems in Austria, Alonso's did, suffering from a MGU-H failure, which saw him revert back to an old 'Spec 2' engine.
Vandoorne has not had an easy start to the season, but has slowly started to look more settled and calm in recent races, even getting the McLaren into Q3 in Monaco, although he didn't actually take part after crashing in Q2.
Speculation is still rife that McLaren will split with Honda and return to using Mercedes power in 2018, after three seasons of below par equipment from the Japanese manufacturer.
Alonso has said that if "McLaren win by September", he will stay with the team, but that seems a long way off for a partnership whose best result is fifth and has only scored two points all season, and are currently last in the constructors'.