Hi BigDave,
What kind of operating system do you use?
The keyboard sends "scan codes" to the computer, which the operating system interprets to decide what character to put in when you type a key. Different keyboard layouts often send the same scan codes, so the character you get depends on what keyboard layout you have set up in the software.
How to type a £ symbol depends on what OS you’re using and what settings it has. On a Macintosh, typing option + 3 will put in a £ character, as tufty pointed out. On Windows, you should be able to use a UK layout, or an “international” layout, and have easy access to the £ character. Otherwise you can hold Alt and type 156 on the numpad (not the number row) to get a pound symbol. I wouldn’t recommend using that method though.