Total Failure - Why?

i would try netting firstly, this will stop birds , especially pidgeons , from eating your crops.also if you net then putting down slug pellets shouldn't harm any birds.
make sure your ground has been properly treated , compost/ manure etc, if there is not enough nutrients in the soil then crops will fail.
you can buy butterfly proof netting, this is the best. birds dont get caught up in it and butterflies cant get in either.hope this helps............steve

Use fresh seaweed on the veg plot, there is not enough salt to harm your plants, but the slugs wont go near it + seaweed contains loads of essential trace elements,
Works for me.

do you have well drained soil-it's been really wet this year the plants hate too much as well as too little water. is it shady? most veg love lots of sun.

What is actually happening to your seedlings - you should be able to see if they are being eaten or whether they are just tumbling over? Could you describe the growing conditions more fully - sun/shade, soil type? And tell us exactly what you have been trying to grow - not everything is successful in any given set of conditions, but SOMETHING should be able to grow!!! I feel for you as I grow veggies - some things work some don't, but something should!

I grow plants on in pots for quite a while before planting them on the allotment or they just 'disappear' too. Make sure that you harden them off properly as the shock of moving from greenhouse or frame to soil will put them at risk of being eaten. Do you use slug pellets? Use them very sparingly and not too near the seedlings as they attract slugs in order to kill them so don't lead them too near. I also think that physical deterrents might help, like fleece or netting. Try beetroot or shallots which slugs don't like much, or potatoes or leeks. Keep trying though.