I don’t know the detail of the weather in the south west gunner, but in the south east we have had a fairly cold spring. Daytime temperatures have varied and the dips at night are less prolonged than winter, but cool days make beans sulk and those few cold hours before dawn are enough to see them off.
Early sowing is a gamble, but I have had french beans out on the plot by this time in other years. As Lettice says, they do grow really fast, so mine are still in the packet so far this year. If spring is cool, I concentrate on the crops that need a long growing period first. I have aubergines and peppers still in the house, tomatoes well wrapped up at night in the greenhouse and the squash and courgettes have just gone into the propagator in the last week.
I will give the beans a feed as suggested, but I think I might start some new ones and plant them out as well as a comparison and see how they compare with each other
May as well
You could sow in March every year, maybe get away with it, maybe not, but think it is worth a go. You could decide to hang on a bit in subsequent years. Either way, it will add to your gardening knowledge and experience and that is a good thing. The weather rarely plays ball and delivers a perfect season, so having the ability to roll with the punches and work round it is part and parcel of growing