Out of interest I sowed a few seeds from each just to see if they are still viable.
The results are in - and yes - all three germinated and are growing. It is very early to be growing from seed, but as I have only sowed a few of each I should be able to keep them growing until planting time once the soil warms up.
I have a small planthouse next to the house. I built it with an old double glazed window and some left over wood. Because it is small, it has been easy to keep warm with a thermostatically controlled heater. I think this is quite economical too - I only want it to be around ten degrees or so. I have an indoor/outdoor thermometer that records the temperature inside and the plan seems to be working well so far!