I managed to get beans the first week in July last year. Was very pleased!! I start mine in root trainers or loo rolls. Planted out mid - late May. Covered with double thickness of fleece held on to canes by clothes pegs and garden twist. Mind you we were lucky with the weather here in East Anglia last year. It was a white variety, saved seed given to me by lottie neighbour, which produced earliest and also cropped the longest (grew 4 varieties.)
Can remember my Dad always trying to grow earliest possible runners it must be in my genes!