Could you dig the area over assuming the, the peas and sweetcorn are gone, by doing so it will expose them to the birds, do this several times, in the future you could try vine weevil killer from one of the garden centres, try growing some rosemarry and lavender plants and use the clippings along where your veg is going to be grown, i have found this to work on other pests, the powerfull scent seems to deter certain pests, so worth a try, julien.

Vine weevils do not normally attack vegetables and Provado is certainly not to be used on edibles.

But vegatables grown in pots, then damage can occur due to vine weevil damage, and the label on provado ultimate bug killer does state that it can be used on certain edibles, julien.

Still seems odd that vine weevils are attacking these Veg seedlings. We have been growing Veg for over 40 years and Vine weevils have been a significant problem as I collect Sedums and Sempervivums. In all that time I have never seen a vine weevil in any veg plant roots.
Unless Cara is re-using old infected compost then they should not be present.
Brassicas are attacked by their own root grubs (cabbage root fly) which would not be affected by V.W. nematodes in any case.
Peas too have an insect which eats the seeds, but mice do more damage to them
I can find no seed or root eating pests of Maize.
I would like to see a picture of these weevils, either adult or grub to be able to help more.
Still would not want to eat anything which had been dosed with Provado myself.

Thanks for the comments so far. I don't think/didn't say these are vine weevils. I think they are some other kind of weevil, but I'm not sure which. I will try to get a picture. The adults look like vine weevils but with one antenna coming from the middle of their head instead of two. They are dull and charcoal in colour and play dead when touched. The adults don't do any harm at all. The roots of every brassica I have grown are eaten and destroyed by the grubs which are small and white. I do plant my veg outside in beds that have the same soil in as previous years but my veg has also been affected when using brand new compost in the greenhouse or in pots.

Sounds like you have more than one problem here. The weevils attacking your Brassicas are not the same as the ones attacking your peas and Sweetcorn.
Have a look here and see if you can see your weevil.
http://www.everythingabout.net/articles/biology/animals/arthropods/insects/beetles/weevil/
Sorry about the VW thing, it was reading Julien's advice which led me to that nasty critter.
May I ask what compost you are using for your seed sowing?

I have put a picture on my photo's of one of the grubs. I found this in one of the peas that I sowed (they do not bother with the peas once they have sprouted/started to grow). The adults that I have seen in the past on the leaves of my cabbages etc looked like vine weevils but with a snout instead of antennas. They didn't look exactly like any of the pics in your link. The grubs that I found in the peas look the same as the ones found in the roots of my brassicas previously. I use vegetable or multi-purpose compost--no one brand in particular.

Trouble is that there are hundreds of weevils in Britain alone. Beetles account for 1 in 5 of all living creatures and the majority of them are weevils.
Not sure now what to suggest. Will carry on giving it some thought.
You might be better asking this on a dedicated Vegetable growing site like Allotment4All. There are some very knowledgeable folks on there.

Thanks anyway for trying to help :)