Thanks for all the replies
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I think what i'll do is to move the rears with 5mm+ on them to the front and the fronts with 3mm- to the rear. Hopefully then i'll have more grip over winter and by next summer all tyres will probably need replacing.
Otherwise the fronts will need replacing quite soon and i dont wanna have to shell out for 2 new front tyres at mo as i'm skint!