Update June 2016: Confirmed still working, as would be a lot of effort for MS to patch billing vs sub websites to fix. Glad it has helped so many
Update 5th April 2015: Still working fine for me 2 months after initially using this. Thanks to all those that have voted hot & confirmed still working for others via comments.
Verified by myself as working in the UK, there's a glitch in behaviour between Microsoft Online Store and Office 365 subscriptions that allows you to buy 1 month of Office 365 Home from the Microsoft Store, but that will upgrade the whole rest of any existing personal Office Personal subscription period + add on 1 month!
What this means is if you picked up a free 1 Year Office 365 Personal with some cheap Windows tablet (like Linx 7) then for just £7.99 you can upgrade that subscription from 12 months 1 user to 13 months of 5 users (each with their own 1TB, soon unlimited, OneDrive cloud storage!) for just that 1x £7.99 amount!
Note before you do this deal add as many Office 365 Personal 1 Year licenses to your account as possible (Stacking up to 4 Years in the future appears to be the safe maximum) and this deal will apply upgrade to that multi-year expiry for same 1x £7.99.
Just make sure to do 2nd part of going in and turning off auto-renewal after initial purchase.
All instructions and more details are on the Deal URL which is thurrott.com/clo…-99
Update from wenttoabetterplace: Possible 100% cashback on this 1 month Office 365 subscription purchase via Quidco! quidco.com/mic…re/
Direct Office 365 Home product URL (But read Thurrott.com
instructions above 1st & Change to 1 month, not 1 year default before buy!) microsoftstore.com/sto…200