The Home Use Program (HUP) is a benefit of Software Assurance, one of Microsoft's volume licensing programs.
It provides a simple way for employers to enable employees to work at home with the same Microsoft products they use at work.
If you are an employee of a firm participating in the HUP, you can get a licensed copy of Microsoft Office 2007 for home use (currently £17.73!) and other Office desktop applications.
Many firms participate. The Metropolitan Police is one large public-sector organisation that is involved there are others.
To purchase software at a nominal fee you complete and submit a web form. You will be sent an authority code to complete the purchase on the Microsoft site.
Apply for Office 2007 and it should ship within 30 days, and you will receive the DVD and product key a few days after that.
Total cost will be 17.31 GBP for a Office Enterprise 2007, 76J-00008 Win32 English Direct DVD Home Use Rights).
If your employer uses Microsoft software and you want to find out if you are eligible for the HUP, contact the Benefits Administrator for the Home Use Program at your employer.
You can find more information at https://hup.microsoft.com/