The current political configuration of the Iberian Peninsula comprises the bulk of Portugal and Spain, the whole landlocked microstate of Andorra, a small part of the French department of Pyrénées-Orientales (French Cerdagne), and the British Overseas Territory of Gibraltar.
Since a peninsula is just an extension of a larger landmass, isn't the exact line dividing the "peninsula" from the rest of the land mass somewhat arbitrary? It seems like it's arguable whether Andorra is on the peninsula or not. Looking at a map, it seems to me like you could draw the line between Bayonne, France, to Tarragona, Spain, leaving Andorra out. Conversely, you could draw the line between Bayonne and La Palma (just south of Narbonne), which would include a decent chunk of France. Disclaimer: I am not a geographer.