The only way I can see it working is if the English can somehow repopulate the city. That isn't impossible, but you're talking thousands of people.
My recommendation would to have the English accept the Jews there, or, and this depends on how successful it can be, find any Berber Christians, and have them be responsible, in exchange for having a good cut of revenue. It's a great place to control the straits (as the English were trying to achieve). If England just stubbornly holds it to finish the Mole, then it becomes a great port for controlling and attacking trade (and nothing wrong with creating a privateer port to take out Mediterranean Piracy.
The trick is yeah, they need allies, and I think that involves not requiring conversion of the locals, but working with and encouraging conversion of Berbers to Anglican Christianity (perhaps that could be the prerequisite for leading a ship, if they were interested).
The idea of an Anglo-Berber Tangiers, half pirate, half trade port sounds fun, but would require those allies, but if the local leadership have the authority to organise diplomatic relationships (of a limited sort) in the area, then they could really engage with the politics of Morocco.
(Plus, I really like the idea of the city being the home of the King of the Crusader Sea Lords - Edward Teach, the Smouldering Prince of Africa)