What is London proof strength and what will be the proof strength of 100 percent Alcohol?

London proof strength is a measure of the alcohol content in spirits, defined as twice the percentage of alcohol by volume (ABV). Therefore, 100 percent alcohol would have a proof strength of 200 proof, as it contains the maximum concentration of alcohol possible. This system is primarily used in the United Kingdom and is less common in other regions, where different proof systems may apply.