...... warmth and light - and of the two I always feel it is lack of light that keeps things back far more than lack of warmth. Deep grey wet skies do not allow anything to grow well, however willing it is. My peas, which should be a metre or so high (bush ones) are barely 6 inches, and flowering bravely, but nothing much is going to happen without more lght.
I think many commercial food growers are going to be in deep troube this year, unless we suddenly get a few weeks of sunshine and light - high food prices this year in the autumn I am afraid.