The new album is called “Third” and it will be released April 14th from Island Records. The tracklist is not yet known and there are 11 tracks and is 49 minutes 13 seconds long. However, we have some info about the names of some tracks from Liberation: In Silence, Hunter, The Burden.
Some fans have recorded some parts from the ATP and you can listen to the new songs from this site.

New songs are very interesting at least, I was totally impressed with them and especially with Machine Gun. Portishead have changed their style in a good way and I’m pretty sure the album will be great. It’s worth the wait.

Although it’s very early, you can pre-order the new album from HMV