my front tyres are on there way out. back ones are fine, do i have to buy all four or can i just get two front ones? myoouk turbo.

 

If they're not worn too much then concensus seems to be that you could fit two of the same type/brand/model. Personally (opinion varies here) I'd put new on the front, they'll catch up (if you drive normally!). If they're worn more than around 4mm difference between front and back (or side-side) theory is they can cause transmission wind-up because of the difference in rolling radius and therefore effective 'gearing' - though once again opinions vary on this one - some say it doesn't matter.
To avoid this swap fronts and rears regularly to even wear - though of course there are arguments on this too!
Seems you can't win here, but I've done 150,000 in two Imprezas applying these rules and not had any related diff/transmission issues. Just allow a few hundred miles of cautious driving bedding in time for new/moved tyres to wear into shape. If they're all the same model I think that's the most important factor for all sorts of reasons....IMHO!