Have you just bought these plants op? and did you get them from a good garden centre which looks after their stock, or a place like B&M, or Aldi - which stick them out in the sun without a drop of water and leave them?
In this weather, even with daily watering, the soil will probably only be wet for the first top 2 inches at the most. Did you soak your plants in a bucket of water before planting as that helps to establish them.
Does the water soak into the soil of the plant you've just watered meaning the soil is well moistured, or does it run off - bone dry?
Also when watering, do you direct the water at the root (as you should), or do you spray the whole plant (which is wasteful of water as it doesn't reach the root)?
Re lavender - as PP said, it likes warm dry conditions, so I never water mine until the very tips begin to drop a little, and even then, it only gets a small amount.
Have you fed your plants any liquid feed (once a week)? I water mine first in the evening, then the following morning, feed them using a watering can, and again, direct it at the roots.
The leylandii will have taken all the goodness from the soil - and probably turned it to dust, so maybe some compost dug into surrounding soil of plant too?
It sounds like you've made a good start - and this summer has been a trial for any gardener, so please don't give up. I love my garden, I love sitting out in it on a night when the air begins to cool, and the bees are still buzzing around. I hope you do too!