A 20 year old man is referred to you from the dermatologists. He presented to them 6 months ago with a leucocytoclastic vasculitis. His eGFR has declined from 80 to 50mls/min/1.73m2. When you see him in clinic he has 3+ blood and protein on dipstic, vasculitic lesions on his leg are healing. His PCR is 300 mfg/mmol (approx. 3g/24 hours proteinuria) and his eGFR is now 35 mls/min/1.73m2. His BP is 140/88. Soluble immunology including, ANCA, ANA, C3, C4 anti-GBM are all negative.
He undergoes a renal biopsy shown below
What is the most likely diagnosis?