I grew Ferline outside last year. Quite a good crop, though not as spectacular as some of the other varieties. We had a bad attack of early blight, but I always spray and most of the plants recovered, although I had to rip out all of the Black Russian.
Ferline didn't seem to be any more, or less, blight-resistent than any of the other varieties. They were all affected to some degree, and all had fruits that I had to destroy, Ferline included.
I don't think any outdoor varieties are blight-resistent. The key things are spraying - a preventative one in early July, or perhaps even late June - and constant vigilance. And on an allotment, try to get your neighbours to do the same. I lose count of the folk who plant tomatoes, don't tie them up or take out the side-shoots and don't spray, and then say, "Yes, mine always get blight!" And then they leave them in situ to rot into the soil and let the wind & rain blow the spores onto neighbouring plots!!!