My penis shaft is irritated and inflamed, additionally the inside is red and irritated also, any idea whats wrong and the best treatment for it?

This sounds like irritation from something you are in contact with.Evaluate any soaps or lotions, condoms, masturbation, sexual activity, new clothing, laundry detergent. If none of that is something new,try stopping one of these at at time to see if it gets better.A cortisone cream might help for the external area,but would recommend you get examined by your doctor to have the right medication.

Herpes, allergic reactions, contact dermatitis, severe yeast infection, superficial skin infection (i.e. cellulitis), and other conditions could do this. Don't try to figure it out online or with self testing. See a qualified provider. One of UK's generally excellent GUM clinics would be a great choice. Good luck.