Hello Grant, I'm Dr. Deb.
I recently came online and see that your question about Charly hasn't been answered. I'm sorry that you've had to wait for a response but if you still need assistance, I'd like to help if I can.
If he is intensely itchy, then fox mange (aka Sarcoptes Mange) is certainly a possibility, especially if you have this problem where you live and he goes outdoors. This LINK discusses this particular problem in detail and also offers treatment options.
I'm not sure what may be available to you in the UK but the least expensive option would be to dip him with Lyme Sulfur if you were able to do so (or have a friend or family member do it). It smells bad and can stain jewelry but it works.
The other options are preferable and much easier: Advantage Multi (LINK)
or Revolution (LINK)
There are other reasons why he might be losing his hair, though, especially if he's itchy and over-grooming:
1. Fleas. You may or may not see fleas since they can hop off and on a cat's body and they can be ingested from all the grooming.Cats can become allergic to the flea saliva and literally one or two fleas can drive them crazy. So, I would want to rule this problem out just to be safe by use of a good topical flea product; either Revolution or Advantage Multi that I mentioned above will work.
This is a link that discusses this problem in great detail: Link
2. Food allergies.
It is usually to food that a cat has been eating for a while--it's not new food. Changing to a hypoallergenic diet may be helpful such as grain-free, or Z/D (available from your vet) or Natural BaXXXXX XXXXXmited Ingredients, Nature's Variety Instincts line, Evo Duck or Venison, Nature's Variety Frozen Raw Medallions (I recommend that they be zapped in the microwave for 10-15 seconds on each side).
3. Pollen allergies to such things as dust mites, mold, grasses, trees, etc although he's a little on the young side for this problem.
These cats may or may not respond to antihistamines (see below) but they almost always respond to steroids which can help with the diagnosis.
4Cheyletiella is an itchy, scaling skin disease of cats caused by infestation with Cheyletiella mites. It is often called "walking dandruff" because when you examine an infested cat, you may see that the "dandruff" is moving. The movement is actually caused by the mites moving around under the scales. Although the mites inhabit the entire body, the scaling and itching often seem worse over the back. Treatment would be the same as for Sarcoptes Mange.
Antihistamines can help in some cases with the itching regardless of the cause.
Benadryl at a dose of 1/2 of a 25 mg tablet given twice daily or
Chlorpheniramine at a dose of 2-4 mg twice daily or
Claritin at a dose of 2.5-5 mg twice daily or
Zyrtec 5 mg/cat once or twice a day
It is important to ensure that the formulations used contain ONLY the antihistamine and are not combination products (e.g. Claritin-D contains pseudoephedrine, which could cause very significant adverse effects in a cat).
Sedation is a common side effect with these kinds of drugs.
5. Ringworm can cause hair to fall out but it's not typically very itchy in most cats. And the areas tend to involve more of the face/head and legs...not the entire body.
I hope this helps; again, my apologies for the delayed response to you. Deb