Just noticed this on the Xbox UK Facebook page:
Mass Effect 3: Extended Cut [PEGI 18, BBFC 18] is available now on Xbox LIVE as a free download. Discover the true impact of your choices...
An expanded ending for Mass Effect 3. Additional scenes and an extended epilogue reveal the impact of Shepard's choices on the future of the galaxy.
Available for PS3 on the 4th July.
For PC users (Thanks to Meowingtons):
On Origin right click the game > Show game details > Shop for add-ons > Extended Cut