The government said an authorized demonstration is planned Friday in a village west of the capital Manama. A travel warning issued Thursday said there may be attempts by protesters to use gasoline bombs and improvised explosive devices during the demonstration.
"As a result there could be clashes between government security forces and protesters," the advisory said.
A Shiite-led uprising in 2011 left dozens of people dead during a government crackdown. The Sunni-led monarchy in Bahrain was criticized for its harsh response to the protests. Human rights groups say several opposition leaders were unjustly imprisoned and tortured while in custody.
The British advisory said there was no direct threat against its citizens, though caution is advised during the course of the next few days.
Human Rights Watch said in a June report there are policies in place to "stifle civic and political groups" operating in Bahrain. Some laws make it so the government can take over or dissolve "more or less at will" civic organizations viewed as critical of the government or its general policies.
Bahrain says it's following reform recommendations outlined by an independent commission of inquiry investigating the 2011 uprising.