and choose Language & Text.
Choose Keyboard
Put a check mark (tick) in the "Show Keyboard and & Character Viewers in menu bar" box
(That step is not essential, just handy)
Now choose Input Sources...
Scroll down the list until you get to British.
Put a tick in the box
Notice in the top right hand side of the Menu bar, that a small Flag just appeared. If it is the US flag, click it and you should have a choice. Choose British, the flag should change and you should now be operating with a Standard British Keyboard. The £ sign should now be where the # mark was and the # mark should now be produced with the Option + 3 key combination.
I installed Lion on my new iMac on Friday and can't get the GB Pound sign, and I can't see how to correct.

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