A pair of gold triple unite coins leads Dix Noonan Webb’s Sept. 26 auction of British coins.

The largest gold coin ever struck in Britain (measured by diameter but not by weight or value), the triple unite of Charles I is one of the great rarities of the English hammered series.

With a face value of 60 shillings (£3), the triple unite weighs 421 grains, about .875 of an ounce. These coins were issued during the English Civil War by two mints (Oxford and Shrewsbury). They show the king (Charles I) on the obverse, with the reverse featuring his declaration of September 1642, in which he promised “to uphold the Protestant religion, the Laws of England and the Liberty of Parliament.”

Charles I made his declaration at Wellington in Shropshire, according to Coins of England and the United Kingdom, published by Spink (also called the Standard Catalogue of British Coins, 46th edition).

Of the pieces struck at Oxford, several minor varieties are known; two are offered during Dix Noonan Webb’s auction of British coins in London, with the difference being the appearance of a group of five pellets on the reverse of one of the examples.

The finer of the two examples offered in the auction, in about Mint State with proof-like surfaces, is “possibly the finest known of this type.” This piece lacks the grouping of pellets.

It has an estimate of £100,000 to £150,000 (about $157,196 to $235,794 U.S.).

The lower grade piece of the two examples, which features the pellets in the reverse design, has “raised die marks in [the] obverse field, a few other minor surface marks,” but is “otherwise Extremely Fine or better.” Its estimate is £80,000 to £100,000 (about $125,757 to $157,196 U.S.).

The British coins auction is one of four auctions the firm is conducting over four days in connection with the Coinex show in London. The British coins offering, cataloged as No. 93, includes 912 lots of British, Irish and Scottish coins from Anglo-Saxon and Norman times to the modern era.

Special consignments include the Charles Collection of Anglo-Saxon and Norman Coins and the Collection of Irish Coins formed by the late Adolf Ganter. In addition, the firm offers the first part of the James Sazama Collection of medieval coins, which will be sold in four parts annually during the Coinex auction through 2014.

The complete catalog can be viewed for free online at the firm’s website, www.dnw.co.uk.

For additional information, telephone Dix Noonan Webb at (011) 44 20 7016 1700 or email it at auctions@dnw.co.uk.

Some additional highlights:

England, King Edward the Elder, circa 899 to 924 silver penny, Minster type, Wulfgar, small cross, church building on reverse, Spink-unlisted (Coins of England and the United Kingdom,< published by Spink), Lot 1012, Extremely Fine and toned.

England, King Edward I, circa 1272 to 1307 silver penny, class 1B, London, “possibly the finest example in private hands,” Spink 1381, Lot 1196, EF, “attractively toned.”

England, King Henry VI light coinage, circa 1399 to 1413 gold noble, type V, London, Spink 1715, Lot 1566, “obverse slightly double-struck, otherwise nearly [EF].”

England, King Henry VII, circa 1485 to 1509 silver testoon, profile issue, Spink 2251, Lot 1573, “profile and other parts of portrait and obverse fields skillfully reworked, otherwise nearly Very Fine.”

England, Queen Mary, 1553 gold ryal, MDLIII, Spink 2489, Lot 1588, “tiny knock in obverse field, otherwise well struck on a full round flan,” nearly EF, “old red toning.”

England, William III, 1701 gold 5-guinea coin, second bust, DECIMO TERTIO edge, Spink 3456, Lot 1624, “a few surface marks, otherwise better than [EF].”

England, Queen Anne, 1706 gold 5-guinea coin, QVINTO edge, Spink 3566, Lot 1627, EF “or better.”

Ireland, John (as Lord of Ireland), circa 1172 to 1199 silver farthing, second coinage, Dublin, Lot 1792,Very Fine.

Great Britain, King George V, 1924 gold Proof or trial piece, by Bertram Mackennal, S-4024, one of three examples known, Lot 1501, “figure 2 stamped before king’s face and scratched in reverse field in front of lion,” “otherwise as struck.” ¦