Watch List notes:

BRITISH COINS, Charles I, Silver Halfcrown, Tower mint, group I, type 1a3, king on horseback left with raised sword, plume to horse's head and crupper, no groundline, initial mark cross calvary (1625-1626) both sides, rev quartered square-topped garnished shield of arms, 14.65g (N 2202; S 2766). A little short of flan on obverse at 6 o'clock, double struck with die flaws, good fine and toned, a scarce type.
from the David Sellwood collection

Estimate: £300-400