External keyboard double functionality

Hi,

I have a macbook pro running osx yosemite 10.10.3. This morning I came out to my office and plugged in my mac book and my external keyboard into it. Now my external keyboard has serious functional issues. Some keys are now performing double functionality. The backspace button types 'f' then deletes, the f key does the same. The enter/return key performs it's functionality as expected however also turns on the caps lock and the caps lock key does the same. The 's' key performs it's functionality however this also acts as the play button (f8).

There are other instances of that. This was working fine the last time I used it (Friday).

I have looked at the keyboard viewer and when I press the key, the other key also presses, e.g. press enter, caps lock is pressed on the keyboard viewer.

Has anyone encountered this?

Regards,

Gary