It's either got a bit cold for them or that sounds like magnesium deficiency.... epsom salts or chilli fertiliser (another mag loving plant) and get it a bit warmer if you can......
Might well be that the compost is a bit light in it as it's expensive to add. Are you finding a lot of twings in your B+Q multi?.... I used it last eyar and it was great, a worthy Which Best Buy, this year it's as dreadful as any compost I've ever used...... still getting most of my seeds through though....
They will recover.
