[Goosegirl]

Similar thing to beans not setting, my toms have lots of flowers but no fruit; however my dwarf French beans in the greenhouse are doing ok.

[mumofstig]

That's lack of pollination. Have you tried tapping the canes/strings to shake them to release the pollen? French beans are self pollinating so should always set well without help.

[JayG]

Apart from wot Mum said, try to keep the temperature down - the flowers can abort in temperatures over 30C (-ish.)

[oldgrunge]

Misting them with water just before shaking them helps too, but as JayG says, they do not like high temperatures.

[lettice]

I normally do this most years, but this year it has been essential with temps 25-32c during the day and 17-20c at night most days this summer so far.

Get yourself a thermometer in the greenhouse and try and keep the temp in the greenhouse below 30c and above 12c.
Each morning I hose all over the floor and all over the outside of the greenhouse glass.
I always water my greenhouse tomatoes and cucumbers at soil level and mist the leaves early evening. I mist then so the leaves do not get scorched from the strong sun.
I also each morning through to late evening on a day when the temp outside is 20+, open the door and peg a bit of netting over the door, with a foot gap at the top to allow the bees to go in and out easily and the breeze no matter how light to enter.
This is additional to opening the greenhouse vents.
I also as they have always mentioned on Beechgrove and all my traditional gardening books, to remove the lower tomato leaves up to the first truss and also remove all the lower cucumber leaves a foot up. This allows the air to circulate.

This will knock a good 7-10c off your greenhouse temperature.

My tomatoes and cucumbers have not suffered at all this year in the greenhouse, have as good a crop as ever. Growing Tigrella, Gardeners delight, Marmande, San Marzano and Amateur in the greenhouse along with Burpless cucumber.

For outside tomatoes, the 30c temp should not be a problem. But mist them once a day also and as above rock them a little each day. Do not allow them to dry out. Always find it best to let the tomato pots rest on soil so the roots can poke through the bottom of the pot to pull up some ground moisture or sit the pot in a pot of water.

[mumofstig]

Ask gardeners, get a lot of different answers 
Personally, I'm not a fan of misting foliage/or the greenhouse at all, it seemed to encourage Botrytis, when I did The toms really suffered badly a few years running before I stopped doing it.

If the temp is over about 12C the doors of my greenhouses as always open (closed a bit if it's windy, of course) I also have auto-vents which open from about 18C. I also remove completely the back top triangular pane of glass, which faces the hedge, this allows a through draught which helps a lot.

I agree with stripping foliage up to the first truss, then when you've picked those, remove the leaves up to the next truss and so on. I seemed to have a lot of foliage on the varieties I grew this year, so thinned some of the upper leaves as well. There still seems to be plenty left for the plants to carry on growing though

[goose]

I am not so scientific and cut off foliage that is so overgrown after a few days away I can't even get into the greenhouse   

[Growster...]

"You don't bring me flowers..."
"You don't sing me love songs..."

Same in our greenhouse, and the echoes of a good Streisand/Diamond song does wonders for our toms!

450Unsb5BCw
Says it all really...