British pound sign mac book pro.

The base symbols for that keyboard translation are shown in the right panel. If you hold the modifier keys, its will switch to the actual characters generated.

For example, hold Option and right-pane display will show the pounds sterling (£) symbol on the 3 key when using the U.S. layout.

US keyboard shows it as Option-3, others vary.

EXACTLY which keyboard translation is in use?

System Preferences > Keyboard > InputSources

the one in use will be shown in the left column

There are fourteen different English keyboard layouts, and at least three keyboard layouts that might be called US.

Which one are you using, EXACTLY?