tomato blight :(

[EeyoreIsh]

I think one of my six tomato plants has blight

some of the leaves have brown patches on them and are yellowing. Two of my other plants are sorting e similar signs.

I've quarantined the sickly looking plant, but what are the chances of is actually blight? Could it be over zealous watering instead?

If it is blight, and tips on how to save my other plants?

I could cry, my poor plants!

I assume you've googled images of blight to be sure? If it is then the brown patches will grow quite quickly and start looking a bit hairy/mouldy and the tomatoes will get blotches on them.
blight info from RHS
I'm afraid there's not much hope if it is blight. But it could be something else like a magnesium deficiency - lots of pix of this on google images and lots of feeding info on the rhs websites etc.