Marvin Lessen, an American working in aerospace and defence, began to collect British coins after moving to Scarborough in 1962.
Leading the January 21 sale at £380,000 – a record for a Cromwellian coin – was a gold pattern broad or 50 shilling piece.
The 50 shilling piece (two and a half times the weight of the better-known 20 shilling coin) ranks among the first milled coins. The design showing Cromwell as Lord Protector is by Thomas Simon (c.1618 to 1623-65) with the coins struck on machinery built by the French moneyer and engineer Pierre Blondeau (d.1692).
Only 12 specimens are now known, with most in institutions.