Watch List notes:

BRITISH COINS, Charles I, Silver Penny, Oxford mint, crowned tall bust left, value behind, legend surrounding, initial mark book, rev large Oxford plumes, legend surrounding, 0.31g (Brooker 965B; N 2477; S 2999). Double struck on obverse, pleasant toning, very fine reverse better and rare.
With old Seaby ticket which notes that the coin was purchased on 3 January 1966 – ticket price £10.

Estimate: £500-700