Great Britain. 1961 Centenary of Post Office Savings Bank. 2½d. black and red. Strip of four. Variety ‘each stamp with black partially missing due to solvent spillage on the “black” cylinder’. Superb unmounted mint condition (with normal stamp for comparison). British Philatelic Association Certificate No. 72,803 (2008). OUTSTANDING AND VERY RARE. AN EXHIBITION PIECE.