If instructors refused to take studes up in "less than perfect" conditions nobody would ever get a licence in the UK!
The flying school will specify minimum conditions beyond which instruction should not be carried out, but beyond that it is up to the instructor - as Gertrude says, it is really down to whether or not a particular stude will get value from the trip.
I have no problem with taking an early solo stude up on a day with poor vis, low cloud base to show bad weather circuits. If you don't push them a little, they don't learn. The trick is not to push them too hard. Crosswinds? You can learn all you like in the classroom looking at what you SHOULD do and how a crosswind affects the circuit, but sooner or later a stude has to DO it.