If you look at the position of the Morning Concert, 4 days to get to Marseille involves travelling the length of the Med. then around Spain and Portugal and through the Bay of Biscay. Marseille to Tilbury should be possible in less than 2 days, a short hop! I´m not an expert . .
Surprisingly, it’s a shorter distance from Port Said at the mouth of the Suez to Marseille, than it is from Sete to Tilbury. 2015nm to 2288nm according to an online shipping calculator.