Your uncle could only be charged with Grievous Bodily Harm (GBH) if your injuries were in this range:
# injury resulting in permanent disability or permanent loss of sensory function;
# injury which results in more than minor permanent, visible disfigurement; broken or displaced limbs or bones, including fractured skull;
# compound fractures, broken cheek bone, jaw, ribs, etc;
# injuries which cause substantial loss of blood, usually necessitating a transfusion;
# injuries resulting in lengthy treatment or incapacity;
# psychiatric injury.
The maximum penalty for GBH (unless it's 'with intent') is the same as for ABH but, obviously, the likelihood of a custodial sentence is higher and the lengths of such sentences are usually longer. (Typically around 2 to 3 years).
It's unlikely that a simple fight between an uncle and a nephew would result in a charge more serious than GBH but if, for example, your uncle kicked your head, it's possible that acharge of 'GBH with intent' could result. This, like attempted murder, carries a maximum penalty of life imprisonment. In practice, most sentences are around 4 to 5 years.
Much of this post is based upon this:
http://www.cps.gov.uk/legal/section5/chapter_c .html
Chris