Is it Potato Blight ?

My first earlie's (Kestrel) and second earlie's (Charlotte) are doing well, deep green tops and some flowering, most of my main crop (Roma) are also looking fine.
My problem is, three of  my Roma plants were turning yellow with brown spots on the leaves. I panicked and asked one of my neighbours (he's had a plot for 36 years) what was wrong, he replied that I had a "bit of blight" due to the weather. On asking what I could do about it , he said pull the damaged bits off, which I did (I pulled the stem off and put into a bin liner then a skip) .

     I remembered reading a post saying that lack of nutrients also led to problems, so I fed them and everything seems fine except for the three original plants. They are slightly yellower than the rest.
 
     This all happened three days ago, my questions are,

1) If it's blight would my other potatoes be showing signs as they are only a yard away from the mains.

2) Would my other mains be showing signs (they aren't).

This my first time growing pot's and obviously don't want all my neighbours hating me for destroying their crops        
           

Thanks Janey,
                    I'll do just that and I won't put the tops on the compost.