It may be that they won't produce caulis because they are what's called "blind". This can be caused by several factors really, most common is planting them too deep, cabbages etc can be planted up to and including the first set of leaves but Cauli (whatever the variety) should never be planted with their first set of leaves in the soil. They also need quite a bit of regular feeding and water so can be temperamental. I had a 50% growing rate my first year and did everything right according to the old timers on my site, they said "that's just mother nature for you"!!
This webpage should get you started, basically I'd also plant stuff that maybe should have gone in in July as you never know we may have a longer summer!
http://nickys-nursery.co.uk/seeds/pages/vegetable-calendar.htm
Just make sure that when you pick up seed packets they are the right variety for sowing at that time of year.
When you say quite shady so long as it gets some direct sunlight you could try the following which I grow in the shaded part of my allotment:
beetroot, brocolli, kale, kohlrabi, lettuce, radishes, rhubarb, spinach (I use perpetual spinach as it doesn't tend to bolt) and turnips (under-rated veg in my opinion)
In response to have small garden which is quite shady, growing veg with limited success. Anybody any tips?
The simple answer is you can't !! But take heart, if you keep the weeds at bay by hand weeding/hoeing regularly and definitely don't let them set seed then each year you'll find that the problem lessens. One thing I do for my leeks in particular is plant them using several layers of newspaper as a weed suppressant
In response to How can I stop weeds forming around my veg.
If it's rabbits then fencing your plot really is your only option, and as a previous poster mentioned you'll need to bury it and bend the top over (the crafty buggers climb over it otherwise!). However have you considered snails/slugs... they decimated my runners last year but fortunately it was early enough for me to get a second set planted
Just an addition here, but if you use a soap based solution (soft soap is best I've found) you must make sure it is spayed underneath and on top of all the leaves etc because, unlike systemic pesticides, it works only by contact with the bugs. The other good thing about soap solutions is that you can use them as often as you like (just don't forget to rinse fruit/veg you've sprayed before you eat it or it'll taste odd !)
As turnips are in the brassica family it could be wood pigeons have devoured your turnip leaves, did you net them?
I use the debris netting on my allotment lot, it is normally used on scaffolding by builders, you can get in on ebay. It's half the price of enviromesh and fleece etc but works wonders at stopping the white cabbage butterfly getting into the brassica cage or laying it's eggs onto the leaves through the netting. It also comes in loads of colours (yes I'm a woman so colour counts!) Please note though you cannot use this for any cage where the contents require pollination, such as fruit, as bees cannot get in either !!
How discouraging for you, make sure you report it to the moderators.