[andyw]

I've found some brown marks on my tomatoes, from what I have read it looks like this could possibly be a lack of calcium.

Just to add the smaller ones are outside and the larger ones are in the greenhouse.

Here is the first pic.

[andyw]

And here is the second, sorry but I cannot add more than one pic at a time!

[mumofstig]

they look as if they've been damaged in some way rather than you having disease or growing problems. Wind may have banged them againt a string or cane 

Calcium deficiency causes blossom end rot, which is invariably at the bottom of the tomato as the name suggests.
As long as you are watering properly, it's not something you'd see anyway.

[andyw]

Ok, I just can't see what could have knocked them especailly the ones in the greenhouse.  I will keep an eye on them.   Thanks.

[CatherineC]

God your tomatoes are huge!  mine are only pea sized!

[andyw]

Why thank you, they were planted from seed on the 17th February.  The smaller ones are cherry and the larger are money makers, just hope they rippen.

[Benandbill]

Could be irregular watering.  I had the same problem last year, just as I was getting lovely big green tomatoes and anticipating them turning red, instead the stems went brown and the fruits got brown patches on them as well.  They didn't turn red.  We didn't have a proper greenhouse which didn't help so when they got too big for the plastic cloche they were exposed to all the elements.  I was told a feed with more magnesium in it might have helped them turn red.

My better half did manage to catch a few before they went brown and made some nice green tomato chutney out of them 

[andyw]

I read a similar issue on the net as well.  I've been watering about twice a week.