When you say Jiffy pots, do you mean the peat pots or Jiffy 7's
If the latter I would say they were just to wet, they don't like cold and
wet conditions. you could try soaking them over night in warm water then
sowing onto compost that is just damp and cover them with paper or
polythene, they will have taken up enough water to get them growing. When
you see the roots starting to push out of the seed then put them into pots.

--
David Hill
Abacus nurseries
www.abacus-nurseries.co.uk