Answer:
In England and Northern Europe there are mosquitoes. In cities they will rarely be encountered. By water, or in mountainous or boggy areas, especially in Scotland and Scandinavian countries rural walkers can be bothered by swarms of very annoying mosquitoes. It is possible to buy mosquito-repelling sprays which prevent them from biting.
Although bites itch they do not carry diseases and do not pose any significant health risk.