It depends on your uni & course. I spoke to Warwick regarding Economics and they say it makes an insignificant difference (barely then). Speaking to more popular universities like LSE however - they mention that it may put you at a disadvantage, unless you had extenuating circumstances that affected your first set results. I'm not sure what course you want to do, but if it's one of the less competitive ones, then you should be okay (applying to top universities - decent ones shouldn't be a problem).