I have a ferry ticket to England on August 14, I’m German and fully vaccinated. As of August 2, I could travel to England and not having to quarantine. But since I’m driving through France, I’m not sure if I still have to quarantine once I’m in England. I haven’t found anything on the web, and calling the Auswärtige Amt in Germany gave me two different answers, both of them not helpful.
The latest situation, as announced in the evening of 4 August is that from 4am on Sunday 8 August people fully vaccinated in the UK, Europe or the US arriving from either France or Germany don't have to quarantine.
Anyone arriving in England before 4am on Sunday 8 August who has driven through France has to quarantine.
The UK government website says "This includes any fully vaccinated individual who transits through France from either a green or another amber country to reach England."
(There is an exemption for the Eurostar from Belgium which travels through France without stopping, but it's not relevant in your case.)