Probably blossom end rot caused by not watering enough or by watering irregularly. Water well and feed at least once a week.

If in the ground, mulch to keep the soil moisture even. If in a pot, adding gypsum or lime may also be helpful, in addition to fixing the watering as Moon_Grower says.

Tugb. in Aberdeenshire Guest will have his/her tomatoes in a greenhouse. Just as we do, this is simply erratic watering and lack of feeding - sorry lad not trying to knock you. If the toms. were in the open ground they would almost be swimming. July has been extremely wet up here... Guest has his toms. in a greenhouse and has not watered regularly - sorry!

Sorry MG! I seem to be putting my feet in it today. I'll be perfect tomorrow...just remember that tomorrow never comes!

Ach, no worries - just try to look at where the person asking the question lives... If in our neck of he wood then assume it os cool and damp - unless I'm complaining of a heatwave (I wish!)

Now, now. Be careful what you wish for! I remember wishing for cool weather in 1990's 125 F summer, which was then followed by the worst frost in 15 years! I do remember that you folks were having a heat wave and a drought just a few weeks ago. I'll just have to also remember that that was then.

No we did not have either a heatwave or a drought in the north of Scotland. June was nice, sunny and, at times even hot and yes himself did water a few times. The heatwave and drought were in the south of England and they still have problems down there. Our maritime climate means that England can be sweltering whilst we are almost freezing. If you look in an atlas you will see we are further north than Moscow it is only the Gulf Stream that allows us to live here in the way we do. Climate change is going to be interesting.

Especially since they keep talking about the Gulf Stream shifting or failing!

Yup