The British government has again denied it had any prior knowledge of fake British passports used by the suspected killers of a Hamas commander in Dubai.
Shadow foreign secretary William Hague said it was "entirely possible" the government had been alerted.
The Daily Mail newspaper claims MI6 and the government received a tip-off.
Mahmoud al-Mabhouh was killed in his hotel room in Dubai on 20 January, a day after his arrival in Dubai. Reports have suggested he was there to buy weapons for Hamas.
Six fake UK passports are thought to have been used by his killers. Israel says there is no proof its agents were involved.
The BBC reports diplomatic tensions have been building between Britain and Israel since it was revealed on Monday that six of the passports used by the 11 suspects were British.
They were clones of passports belonging to men who have dual British and Israeli citizenship.
Mr Hague told the BBC it was "entirely possible" the government had been alerted to their use in January.
The Daily Mail on Friday quotes a British security source who claims MI6 and the government were told of the operation.
A Foreign Office spokesperson said it was "not correct" to state Britain knew in advance about the passports.
Interpol has issued arrest notices for 11 suspects, although it admits their true identities are unclear.
Meanwhile, the BBC reports two Palestinian suspects are being questioned about the murder. Police said they fled to Jordan after the killing, but were extradited back to Dubai on Sunday.
The BBC is also questioning why Mr Mabhouh went to Dubai without his security guards, and possibly under his own names.
A correspondent asks if the hit team's detailed knowledge of his itinerary, the lack of bodyguards and the possibility he was comfortable travelling on his own identity, mean Mr Mabhouh was served up to his assassins in Dubai by people he trusted?