At Silverstone, as soon as Lewis Hamilton had a) lost the lead to Charles Leclerc’s Ferrari as his momentum was checked by his collision with Max Verstappen and b) incurred a 10sec penalty for the incident (to be taken at the tyre stop), his race strategy was largely predefined.
With Hamilton unable to pass Leclerc on the restart, and with Leclerc setting a pace quicker than the cars Hamilton was trying to clear, Mercedes needed the Ferrari to stay out there leading, with Hamilton just following. The longer they could do that, the more time they’d pull out on the pack and therefore the fewer places Hamilton would lose when he took his 10sec penalty in the pits.