* It's a contracted form of "will be able to do": The phrase "will do" is actually a shortened version of "will be able to do." In British English, this contraction is common and understood, even if it's not grammatically explicit.
* Emphasis on willingness: Using "will do" emphasizes a willingness or readiness to perform an action. It's a way of saying "I'm ready to do this" or "I'm going to do this."
* Similar to "will be doing": In some cases, "will do" can also be understood as a shortened form of "will be doing," indicating an action that will take place in the future.
Examples:
* "I will do my best." (Meaning: "I will be able to do my best.")
* "Will you do the dishes?" (Meaning: "Will you be able to do the dishes?")
* "I will do that tomorrow." (Meaning: "I will be doing that tomorrow.")
Note: This usage is more common in British English than American English. In American English, "will" is more often used with a direct object, such as "I will go" or "I will help you."
Overall, "will do" in British English is a shortened, idiomatic way of expressing willingness, readiness, or future action. While grammatically it's not strictly "correct" in a literal sense, it's perfectly understandable and common in British English.