It's not been banned, but I do think it is going to be removed from the organic usage list soon. Why after all these years, I have no idea. Science changes quicker than the wind, and then back again, usually under political and commercial lobbying, and Bordeaux mixture is a perfect example. I have always prided myself on organic growing apart from the odd slug pellet, and they're history in the next month once my 3 year old bottle runs out.
Bordeaux is effective on greenhouse tomatoes, there's no doubt, but like others have said, maybe a bit early to spray. Last resort reactive spraying is my method. Looking at the forecast, if we get through this weekend without a Smiffy, we'll be safe into July.
I'm changing my practice this year and I've gone for a dual running approach this year. Half my greenhouse tomatoes are in the border, and half are in pots on staging, ready to be redeployed if necessary. Having said that and having always grown my greenhouse tomatoes in the border, it has been interesting that my potted gardeners delight and tumbling toms high up on the staging this year are not suffering from the leaf condensation that allows the spores in while my border plants are peppered every morning.
Borderowl ... it is difficult to tell from a picture, but it does look a bit like the botrytis I had to manage last year. Iif it is one lone plant, and all the rest are fine, I would be hopeful and say it's not a blight. I would still carefully move it somewhere else though if I were worried.