Keyboards with #. £ and $ started appearing in the UK at about the same time as 8-bit characters were becoming popular on mini-computers and PCs (the very early '80s). See my earlier post about keyboards and 7-bit ASCII to understand what happened before that time.
Once 8-bit code-pages became popular, the lower 128 (well, 95 really because of the 33 non-printing characters) code points of almost all internationalized code-pages were the same as US ASCII (X3.4-1986), and any character not in US ASCII was pushed into the top 128 (well, 127 really, because position 255 was normally delete or something).
This meant that there were many, many code pages to cope with different characters for different languages, not just the UK, and a corresponding set of keyboards. Here is an interesting page from IBM, who IMHO were the first company to really start standardizing keyboard layouts for different countries (the 'enhanced' keyboard many of us will be typing on is basically an IBM layout from the PC-AT era, although DEC's international LK-201 keyboards were of a similar time-frame).
Note the references to the 101, 102 and 106 keyboards pre-date the addition of the 'windows' keys.