As a general rule, most plants don’t do much when the temperature of the soil is below 8 degrees Celsius so warming the soil has real benefits. You can basically move the season ahead by a month. Sow in March but provide April conditions.
This video follows on from his video on how to build a hotbed
Soil Warming Methods
One method that Simon doesn’t cover is laying down black plastic and I agree. It’s ugly, not eco-friendly and often ends up blowing around and being a nuisance to others.
In the allotment shop we’ve got a good range of Cold Frames, Cloches and Rhubarb Forcers along with fleece etc.