Please use Firefox to run this script - Chrome works but has memory problems with large batches. Firefox should be able to generate a few million email/password pairs. I don't know what will happen if you run this in IE. Or Safari. Caveat emptor...
This script generates passwords and email addresses in the following format: password,fName.sName@company.co.uk
Running this script should start a download in your browser. The generated file is in csv format, but by default it does not have a file extension. This file can be opened using Notepad++, if you wish to inspect its contents. If you want to use this as a spreadsheet, rename your downloaded file to filename.csv and it should open in Excel/Google docs.