Question
Hello. What is the clear sticky substance that seems to be seeping out of the leaves and stems from some plants in my garden?  I've noticed it on my rose plants and blackberry bushes.
It's very hot here in England at the moment, i presume this is the cause.

Answer
Sounds like the problem is aphids (a soft bodied insect that sucks the plant juices) the sticky is an excrement called honeydew--a substance that is high in sugar content. You will need  to control the aphids and the sticky will go away. Not sure of the set up in England but if you have them check with a nursery or garden type store for an insecticide for aphids and spray the foliage completely.