What is the instrumental piece/song playing in the movie 28 weeks later?

Question

theres no singing, but it plays a couple of times. i have it stuck in my head

Answer 1

At a guess, the track you are referring to is the one which is used as the signature theme in this movie and the prequel (28 Days Later).  It starts quite slow and soft, but then a thudding bass starts and it builds up and suddenly drops off again if it's the track I am thinking of.

In 28 Days Later the tune is called  "In The House - In a Heartbeat"

In 28 Weeks Later the tune is simply called "28 Theme"

Both tracks are by the same composer/artist: John Murphy

You can hear a 30 second sample over at Last.FM (no account needed), whihc might help but it isn't very long I admit.  Link below