No British holidaymakers are thought to have been killed in the latest bomb attacks on Bali.
But the possibility Britons had been killed could not be ruled out, the UK ambassador to Indonesia said.
One Briton was badly hurt and one less so, he said. A helpline has been set up for worried relatives on 0207 008 8765.
Malaysian fugitive Azahari Bin Husin, a former Reading University student, is suspected of helping mastermind the bombs, which killed 19 people.
"We're still contacting hotels and others to make sure there's no-one missing," ambassador Charles Humfrey told BBC News.
He said there were still 10 unidentified bodies at the Sanglah Hospital mortuary.
"So we cannot give you absolute certainty that no further Britons have been killed or injured but so far we know just of these two Britons who've been injured," he said.
There are approximately 1,000 people currently in Bali with British tour operators, according to Keith Betton, from the Association of British Travel Agents.
Consular staff have flown to Bali from the British Embassy in Jakarta and have visited the two injured Britons.
A woman with dual British/Australian nationality has been airlifted to Australia for further treatment.
She was seriously injured alongside her husband and the pair were taken out together, the Foreign Office said.
Foreign Secretary Jack Straw said Britain had been in touch with the Indonesian government about the bombings.
"Messages have been sent by the UK as EU presidency and also bilaterally to express solidarity with the Indonesian people," he said.
The Indonesian security forces had their support "in their efforts to identify those who perpetrated these atrocities", he added.
On Sunday, Defence Secretary John Reid denied the latest Bali bombings had a direct link to the invasions of Iraq and Afghanistan.
Speaking in the northern Afghani city of Mazar-e-Sharif, Dr Reid said: "These people who spread their murder and mayhem were carrying out attacks before the operations in Afghanistan and Iraq and people have to be prepared to accept that they may continue to do so for some time."
Revised travel advice on the Foreign Office website urges travellers to Bali to "exercise extreme caution at all times because there remains a high threat from terrorism".
Tony Blair has offered support to Indonesia after the blasts
The number of British tourists visiting the holiday island, already down since the Bali bomb blasts of 2002, is expected to take another dip following the latest attacks.
Twenty-eight Britons were among the 202 people killed in the 12 October 2002 bomb attacks in Kuta, blamed on Islamic extremists.
The Foreign Office said its helpline had been "extremely busy" and was currently receiving about 120 calls an hour from people concerned about friends or relatives in the region.
"We are taking information about British citizens and passing those details on to our officials on the ground in Bali," a spokesman said.
Indonesian terror official Major General Ansyaad Mbai named Malaysian fugitives Azahari Bin Husin and Noordin Mohamed Top as suspects in Sunday's bombings.
Azahari Bin Husin completed a doctorate at Reading University in the 1980s and is reportedly a bomb maker for the terror organisation Jemaah Islamiah.
He and Noordin Mohamed Top have been on Indonesia's most wanted lists since the attacks in 2002.
In a statement, Reading University said Husin had appeared to be a "completely normal student".
Meanwhile, Prime Minister Tony Blair said he was writing a personal note to Indonesian President Susilo Bambang Yudhoyono offering support and sympathy.
"Our thoughts are with the victims and their families," he said.
The blasts took place just before 2000 local time (1200 GMT).
Two blasts went off at Jimbaran - a seaside area packed with restaurants. Another was at Kuta beach, the area most popular with Western tourists.