Is it true that because of Proportional Representation in the UK MEP elections, if we want to keep out the BNP?

Or any other minority party, we have to vote for another minority party and a vote for Tory, Labour, Lib Dem or Green is a 'wasted vote'? I don't want to discuss voting BNP or not, but I had a leaflet through my door today claiming this, from another minority party, and I don't understand enough about PR to know if there is any truth in this, or if it is flannel of the first order?