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.
Leclerc wasn’t the priority at this point – how many cars might jump Hamilton when he took the penalty was the first order of business. They would have to save the fight with Leclerc for later. Because fighting past Leclerc – who would always have re-passed at the stops anyway, due to the penalty – would be at the expense of tyre life, enforcing an earlier stop for Hamilton before he’d pulled enough time out on the pack.