From Ancestry.co.uk's Karen Reynolds via the company's blog (and subsequently via Chris Paton's blog):
We’re excited to announce that from 7th -14th November 2010, you can search and view the original historical documents from our three most-used military collections completely free.
We’re making the following collections free -
British Army WWI Service Records, 1914–1920
British Army WWI Pension Records, 1914-1920
British Army WWI Medal Rolls Index Cards, 1914-1920
The free period will end on Sunday 14th November at midnight so make sure you get all your searches done before then!
Look out for more information this Sunday.