A lot depends on how deep it is. If you run your fingernail across it, does it snag in the scratch?
If it doesn't, then T-Cut will probably do the trick. Be sure to get the right one, depending on whether the car is a metallic/pearlescent or a base colour.
Other than that, if it's a base colour then give it a shot. I've had some success loading the scratch up with paint so that it's a little proud, leaving it a couple of days to harden and then gently t-cutting back so that it's flush with the original finish. Just take care not to rub too hard with the t-cut on the existing paintwork, as it is possible to go through to the primer.
If it's a deep scratch on a metallic, then you'll need to get it professionally resprayed if you want it to look half decent
Don't leave it too long. It's a little known fact that primer and even metallic base-coats are porous, and if you leave a scratch like this for too long, eventually the metal beneath will start to rust. If it's going to be a while before you can get it fixed, then buy a bottle of laquer and paint over the scratch to give it some protection. It won't look good, but it'll protect the bodywork.