my cucumber seedling last year

I would be planting mine (and chillies, beetroot,) if T&M could be bothered to post my seeds. (see other thread!!!)
I've ordered a white cue to try....

I haven't planted mine yet either but, to be honest, I am trying to learn from my mistakes.  I planted lots of things way too early last year and had lots of stress trying to keep them warm and with enough light!  This year I am relaxing a bit and will plant my cucs in a couple of weeks time.  Hopefully they will still be successful!

that's the mistake I made last year Trillium, won't make it again.
Mid April the first couple will be sown, and another couple 2 weeks after that.
If the first 2 curl up their toes, I'll still have two on the way 

I'm surprised anyone has started cukes yet as they're so cold sensitive that unless you've got a warm greenhouse for them, they'll sulk if they simply don't die off. I won't start mine until beginning of May.

yip 2nd week of may here as always.

Planted mine about 10 days ago and they romped out!!  They are huge already and have been potted on and are in a greenhouse in my greenhouse (which is a very cunning plan to save on heating!)

when should I plant out as my pack does not tell me!

As late as possible.  I keep mine in the Conservatory (unheated but warmer than the greenhouse as attached to the house, natch!) as long as possible before moving to the cold greenhouse. They hate the cold.

Last year sowed 02-Mar, planted in Greenhouse on 25-May (first fruit 16-May ) - I think they were about 4' tall when planted.

If outdoor cucumbers then you need to delay even longer - I would recommend past last frost and another couple of weeks more to let the weather warm up some more.