A very quick hint for all users of Microsoft Office 365, whether on Mac or Windows. A monthly subscription in the UK is £7.99 (£95.88 a year), there is the option on the Microsoft website to sign up for their yearly subscription for £79.00 (saving £16.88). However, the cheapest way I have found of paying for my Microsoft Office 365 subscription is buying a Pre-Paid yearly subscription card from Amazon, this will give you exactly the same access to Microsoft Office 365 (5 PCs or Macs, 5 tablets including iPad, Android or Windows, plus 5 phones and up to 5 users) but at the moment the price is £55.59 (£40.29 a year cheaper than the monthly subscription and £23.41 a year cheaper than getting the yearly subscription directly from the Microsoft website).
Once you have received your code from Amazon log into your Microsoft account, click on your account name in the top right and select View Microsoft Account, click Service & subscriptions in the Account bar then click Payment & billing under Office 365 Home, you will then have an option to Redeem a card or code. Saving some money is as simple as that.