No great change in this plant in March, although I have come to the conclusion that poor quality of the soil is responsible for the slow growth and stunted leaves. It seems that the plants that have suffered from deteriorating soil quality are all large rooted species and I suspect that due to the increased growth rates inside my polytunnel, the roots are compressing the soil more rapidly than would normally be seen, so the soil is becoming too dense and not allowing further root growth, aeration of the soil or absorbtion of nutrients and water by the roots. It looks like I have a lot of re-potting to do, so hopefully this will have positive results.