what fruit or veg will grom in boggy soil

Sorry Fzorla you could try rice but no other veg is going to grow in permanently wet soil. There are lots of plants you can grown, take a look at http://www.letsgogardening.co.uk/Information/BogPlants.htm

Fzorla, once upon a time we used to have a smallholding in Buchan and I am quite familiar with the situation that you have. Unfortunately, I just cannot think of anything in the way of vegetables and fruit that would prosper in your ground unles it can be drained.
Mg is not being facitious when she mentioned rice because it is grown in high mountain regions, but I have never heard of it being trialed in Scotland.

I really wish I could think of fruit and veg you can grow but...

Lemon Grass! At least in the summer.

Actually, you could seriously try growing Watercress or even Wild Rice (Zizania aquatica), which isn't really a true rice at all.

I was thinking watercress, but Fractal got there before me! I think the answer might be raised beds so that the drainage can be controled and the veggies will be well above the water table?

Fractal did? I think even with raised beds there would be a problem...

watercress

When we had the smallholding there was a burn at the back that was almost choked with watercress. They were strong plants with good leaves but we never ate any of it. The reason for this is that we were concerned about the possibility of liver fluke in the water. Many of our neighbours kept sheep which had access to the water and liver fluke can be passed from sheep to humans via water.
That appart watercress is hardly an exciting vegetable though I still can't think of anything better.

I still think a proper bog garden is the answer and to heck with any fruit and veg. in this case

Is it possible to access this watercourse at the top of your land, Fzorla and divert it round the edge of your field and then drain the ground? The ground will be sour and acid after you have done this but at least you can then start to work on improving it.