It may be that they're just too close in there--it does need more space. I usually do single stems at 6"ish and double/triple at 10-12" spacing depending on where they're at.

The spotting looks more like a sunburn to me. What's the varietal out of curiosity?

Thanks for reply. Variety is Bush Basil. I know that they would be better off with more space but think they should grow ok like this too. Dont think that leaves damage is from sun. We had sunny weather for last couple weeks but not very strong. I live in UK, not much sun in here. Now is more wet weather and it seem to get worse. Thinking it might be too much water what makes them leaves brown. Will post more close up pics later. Any ideas please share. Thanks

Thin them out. Too many plants too close together.

I've grown the Greek Bush Basil and IIRC it spread about 10" so I, too, would thin these.

jan