Little dark grey flies

[johninblackpool]

Hi Folks

Hope someone can help
Earlier this week i took the covers off my raised beds for the first time and within an hour my lettuce and spuds were covered in hundreds of little flies, they were dark grey, not sure if these are what you call blackfly.
I washed them away with water and recovered them again,
Today i took the covers off again and check to see if there were any more flies and all was clear but within an hour they were covered again
Any help greatly appreciated

ps. I have read that people use soapy water to keep flies off, do you think this will help

Cheers
John