Hi all this is probably a really stupid question, but my timing is awful so I'm trying to practice with a metronome. Only problem is I can't hear it while I'm playing, and I tend to just override it and go with my own rhythm. Any tips for keeping in time?

Get an electronic one with a light is one option.
Also, some have ear pieces, You could get one with an ear piece and then the sound will be in your ear like a click track in a recording studio.

An exercise you can do is have the metronome going when it is quiet and your a piddling around or studying. This will get your sub-conscious used to an even tempo.

And be sure you are not eating your foot when you are practicing (with or without the metronome).

<Added>

That should be "beating" not eating your foot. looks like I put my foot in my mouth with that mis-spelling.

You could also get a mute for you violin so you can play quieter and hear the metronome better.

Thanks guys I'll give it a go.