This is an attractive, uncommon example of international, short-paid, business mail(not a complete letter) sent from London District Post Office, #14 with an initial payment of a Penny Red(a pretty good strike of the diamond-in-bar, numeral cancel, "14")! It was dispatched for Nice, Kingdom of Piedmont-Sardinia, on December 20, 1851(Note the black, CDS cancel at the back from the London District Post Office #14)! The sender was a David Smith. Intriguingly, the addressee appears to have been a Jewish businessman(a purse-related business(?)), a Judah Messiah! It looks like a forwarding agent, Bawmary(?) & May, was used to facilitate the delivery of this international mail, as well.
To continue, the Penny Red stamp(w/ 3, wide margins, and most(or all) of a fourth one) is in very good condition! From London, the mail was put on a French ship on 12/21/51, and taken across the English Channel(Note the superb CDS from that paquebot!). The mail finally reached Nice on December 25th(Note the straight-line, receiving cancel(in Italian!) at back.), where the charge of 10-Centimes would have been paid.
Lastly, as for the partial wrapper, itself, it's in pretty good condition for something over 172 years of age! It's pretty clean. There are the usual creases here and there. Noted imperfections aside, international, short-paid mail sent with Penny Reds from England are not seen everyday!