Keyboard MacBook Air - cannot get pound sign

If this is the U.S. keyboard, U.S. International PC, or ABC-Extended keyboard input devices, then the correct shortcut for £ is option+3. Your shift+3 keystroke would be correct on a British (GB) keyboard.

PamfromSussex wrote:

When I press Shift and key 3 I get # instead of pound sign. Help please.

Go to system settings > keyboard > text input > edit > all input sources and make sure the only item on the list is called "British". Use the minus button at the bottom to remove everything else.

PamfromSussex wrote:

I had previously gone into settings and changed to UK keyboard but that did not help.

You can't change the active keyboard via settings. If you want to avoid accidentally winding up with US active again, which can easily happen if you hit the wrong key, make sure you remove US from the All Input Sources list and that only GB is on it.