That way prisoners wouldn't get the vote

Why is this a good thing? Prisoners are still citizens. Disenfranchising them only serves to further alienate them from society.

Time and again the ECHR has served as an important check on breaches of the European Convention by the UK. But a few examples:

http://en.wikipedia.org/wiki/Smith_and_Grady_v_United_Kingdo...

http://en.wikipedia.org/wiki/Saunders_v_United_Kingdom

http://en.wikipedia.org/wiki/R_v_Bournewood_Community_and_Me...

http://en.wikipedia.org/wiki/Sutherland_v_United_Kingdom