British Foreign Secretary William Hague said London was committed the funds in 2011 to support the tribunal probing the 2005 assassination of former Lebanese Prime Minister Rafik Hariri.
"It is important that international justice be done and that we hold those guilty of serious crimes to account," he said in a statement.
Damascus and Hezbollah are widely believed to have played a role in the 2005 slaying. Saad Hariri, the slain leader's son and current prime minister, absolved Damascus recently and Hezbollah said it believes Israel played a role in the killing.
The Wall Street Journal reportedly recently that at least two members of Hezbollah could face STL indictments by the end of the year. Hezbollah warned it would react strongly to an indictment.
Hague stressed that only through the work of the independent inquiry can Beirut hope to move past an era of political turmoil.
"This is the only way to ensure long term stability in the country," he said in a statement.
Washington followed suit recently with its own STL contributions and lawmakers also lifted a ban on military aid for Lebanon.