I've heard about William the Conqueror's invasion bringing the then-current French language to Britain, but what about the fact that the Romans occupied Britain? In other words, what percent of the Latin in English came from the occupation of Rome, and what percent came from the Norman conquest?

It's not. It's derived from Germanic languages.
The romance languages (Portuguese, Spanish, Catalan, French, Italian, Romanian, Friulian, etc.) are derived from Latin, but not English.
English has words derived from Latin, but only because English speakers have a great habit of borrowing words from other languages.
Germanic languages are not derived from Latin, they are derived from the same languages as Latin, but they formed into two separate branches. I know Modern English (and really most modern languages) are a hodgepodge of influences. But I've noticed that people think English derived directly from the language of the Romans.

Weren't the Romans from Italy? And Romans spoke Latin..

I've heard about William the Conqueror's invasion bringing the then-current French language to Britain, but what about the fact that the Romans occupied Britain? In other words, what percent of the Latin in English came from the occupation of Rome, and what percent came from the Norman conquest?

What happened to it being spoken by the Romans and other Persian cultures?

It's not. It's derived from Germanic languages.
The romance languages (Portuguese, Spanish, Catalan, French, Italian, Romanian, Friulian, etc.) are derived from Latin, but not English.
English has words derived from Latin, but only because English speakers have a great habit of borrowing words from other languages.
Germanic languages are not derived from Latin, they are derived from the same languages as Latin, but they formed into two separate branches. I know Modern English (and really most modern languages) are a hodgepodge of influences. But I've noticed that people think English derived directly from the language of the Romans.

i have a question "Why did the Romans speak Latin but not Roman?". By the way, is my question grammatical ?,is the word "but" optional or obligatory?. Thank you.