Actual bodily harm includes any hurt calculated to interfere with the health or comfort of the victim: such hurt need not be permanent, but must be more than transient and trifling.
e.g.
• loss or breaking of tooth or teeth;
• temporary loss of sensory functions, which may include loss of consciousness;
• extensive or multiple bruising;
• displaced broken nose;
• minor fractures;
• minor, but not merely superficial, cuts of a sort probably requiring medical treatment (e.g. stitches).
Grievous bodily harm means serious bodily harm.
e.g.
• 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.
http://www.cps.gov.uk...s_against_the_person/