Number 10 's door is the product of the renovations Charles Townshend ordered in 1766 ; it was probably not completed until 1772 . Executed in the Georgian style by the architect Kenton Couse , it is unassuming and narrow , consisting of a single white stone step leading to a modest brick front . The small , six-panelled door , originally made of black oak , is surrounded by cream-coloured casing and adorned with a semicircular fanlight window . Painted in white , between the top and middle sets of panels , is the number " 10 " . The zero of the number " 10 " is painted in a very eccentric style , in a 37 ° angle anticlockwise . One theory is that this is in fact a capital ' O ' as found in the Roman 's Trajan alphabet that was used by the Ministry of Works at the time . A black iron knocker in the shape of a lion 's head is between the two middle panels ; below the knocker is a brass letter box with the inscription " First Lord of the Treasury " . The doorbell is inscribed with " PUSH " although is rarely used in practice . A black ironwork fence with spiked newel posts runs along the front of the house and up each side of the step to the door . The fence rises above the step into a double-swirled archway , supporting an iron gas lamp surmounted by a crown . '' ( See The Entrance Door c1930 : As seen from the outside ) '' After the IRA mortar attack in 1991 , the original black oak door was replaced by a blast-proof steel one . Regularly removed for refurbishment and replaced with a replica , it is so heavy that it takes eight men to lift it . The brass letterbox still bears the legend " First Lord of the Treasury " . The original door was put on display in the Churchill Museum at the Cabinet War Rooms
IRA mortar attack in 1991
Downing Street mortar attack
10 Downing Street