Great Britain 1862 6d Deep lilac Plate 3 (Watermark inverted), SG83wi.
A very fine unused large part original gum left hand wing margin block of 4 lettered CE-DF. Some slight perforation faults at foot of DE, nevertheless a spectacular multiple with lovely intense colour.
The 2005 British Philatelic Association Certificate of Authenticity fails to mention the inverted watermark.
The Stanley Gibbons specialised catalogue (last published in December 2011) lists the value for a single stamp at £8,000, pricing this block of four at a sizeable discount to the value of the stamps as singles despite being much rarer.
GB Specialised Catalogue Number: J71(1)e.