The British High Commission said it was is in contact with Nigerian authorities following the detention this week of the pair in southern Bayelsa state.
Nigeria says an estimated 200,000 barrels of crude oil worth more than 20 billion dollars (£12bn) on the international market is stolen daily. Analysts say high-ranking politicians and military officers also benefit from the thefts.
President Goodluck Jonathanannounced this week that his government had earmarked one billion dollars (£600m) to fight oil theft.
Nigeria is Africa's biggest oil producer of around 2.2 billion barrels a day.