Debatable whether it's made any difference compared to the other thousand variables involved in whether a country is doing "badly" or not, and compared to the other electoral options available.
You are totally misunderstanding what is going on in your own country and then reaching for irrelevant solutions. There isn't any swing from left to right, the entire political edifice has moved to the left in the past 30 years and keeps going. The choice now is between two left wing parties (very left wing by historic, British standards), plus some other options that won't win but are basically the same. In other words, the problem is with parties and the way they are so easily captured. PR doesn't solve this problem.