System Preferences > Language & Text > Input Sources. There, check
Show Input menu in menu bar, and make sure the first item in the list -
Keyboard & Character Viewer is also checked.
Now you can open the
Keyboard Viewer from the new icon in the menu bar. Green keys are "dead keys" (i.e. they modify the next character you input, like
´ + e = é). Press shift and/or alt to view the characters you enter while pressing those modifier keys.
I assume that the ` key is -- without modifiers -- displayed in green. If not, try changing your layout temporarily, maybe it will snap back.
Otherwise, check a few other applicable
Input Sources in the same system preferences pane (British, US, US Extended and US International PC all match your printed keyboard layout except #/£) and switch between them in the list for the new menu bar item. The Keyboard Viewer will update immediately, so you can look for a layout you like, in terms of dead keys and even characters you type while pressing alt (those not printed on the keyboard).
(I have an international english keyboard, so I don't have first-hand experience with your layout)