If he has a strong odour he may have yeast on the skin, try bathing with either malesab, Quistel or Neem shampoo.
When you say you have gone the 'food route' did you feed a novel protein source?
Spray the house monthly with Indrex to kill dust mites and damp dust daily.

heres the labs prices for testing, obviously your vet will also charge for taking the bloods, consultation etc.
http://www.ctdslab.co.uk/allergy.html

Hi, thank you, it was the vet who suggested taking him to a special allergy clinic at a cost of £900!! but I will ring him and ask if he would do the blood test. Thank you.

Dont know if any help but we had a shepherd come in with same symptoms and owner told us only way to stop it was keep on food with protein of less than 17% and it worked well.

Oh no really? How can that be remotely good for health?!

Dogs are carnivores!! They need to eat meat with bone, and lots of it, preferably fresh!!

In my experience with stray dogs here, the quickest way to get a dog in optimal condition and fast is with a prey-model raw diet with no carbs whatsoever as it's much easier on all the organs so the body can utilize all of the nutrients to concentrate on health. Carbs put an extra strain on the digestive organs and in particular on the kidneys which struggle to process them together with the poorer quality protein typically found in all dog food.

We get dogs here that have all manner of skin complaints and they clear up really quick when switched to their natural species appropriate food.

I too would recommend and I do use Neem Shampoo to help with skin health - I get mine from NeemGenie.co.uk

Hi, I am wondering if you have thought about yeast infection? Symptoms can be intense itching...just a thought?
My cavalier has had food intolerances since a puppy, he is now 3 yrs old and I have finally found a food that suits him after much trial and error! He now eats Nature's Harvest fish and brown rice and his digestive system is settled...!
If he has anything else...such as treats (other people give him!) he gets a very itchy red mouth that he rubs like mad on the carpet and his earwax gets worse and sore. I know he has to remain on this diet forever which is a good quality food, but i do cook him fresh fish and potato and veg too. It has been a long road and lots of trial and error...and you have to be strict..even when he improves, stick to the diet.
I hope you find the cause of your dogs itching as it must drive them mad!!
good luck
x

Have you thought of trying this?,I've ordered the
spray for Summer,here is the link
www.aromesse.com/petnat/dermacton.php
It looks pretty damn good,I'm also trying
garlic and fenugreek and mixed vegetable
tablets from Dorwest Herbs,I only started them
on Thursday,so I've got to give them time,but
really looking forward to trying the spray.