Nathan Matthews, 28, and Shauna Phillips, 21, are reportedly being held by police over the 16-year-old's murder, but police must either charge or release them by this afternoon.
George Osborne said HSBC must deal with the "legacy of the past" as he indicated new laws could be needed to deal with tax evaders.
The Chancellor said he had been unaware of allegations that the Swiss arm of HSBC had colluded in tax evasion at the time its former chairman Lord Green was appointed as a trade minister.
Speaking on Radio 4's Today programme, Osborne said the Government was "looking at further changes to the law to make sure that we have a tough regime".
"If there are deficiencies in the law, if it's difficult to bring these prosecutions, then we should change the law," he added.
An ex-Royal Marine killed while fighting against Islamic State militants alongside Kurdish forces originally headed to Syria to provide medical aid, an MP has said.
In an interview with Sky News, Dan Jarvis, who represents the Barnsley Central constituency, said he believed Konstandions Erik Sculfield had travelled to the troubled region for "honourable reasons".
He urged anyone else with "legitimate concerns" about Islamic State not to travel to the Middle East, and instead support charities working in the region.
Becky Watts' stepbrother and his girlfriend are reportedly being held by police over the 16-year-old's murder.
Police are questioning a 28-year-old man and a 21-year-old woman in connection with the alleged killing, which turned into a murder inquiry when officers found body parts at a house yesterday.
Nathan Matthews and Shauna Phillips have been named in several newspaper reports as the pair.
Officers were last night granted a further 24 hours to question them but must either charge or release them by this afternoon.
A further four men and one woman have also been arrested on suspicion of assisting an offender.
Nigel Farage said he wants to bring immigration into Britain "back to normality," with numbers similar to those seen before 2000.
"Net migration into Britain varied between about 20,000 and 50,000 a year," the Ukip leader told Good Morning Britain.
"The effect of Ukip policies will be to bring us back to those sort of numbers," he said.
"What we're pushing here represents a drastic cut."
Around 100 people from Western countries - including a number of Britons - are believed to have gone to Syria to join Kurdish forces battling against Islamic State militants.
The figures come as it emerged ex-Royal Marine Konstandinos Erik Scurfield, from Barnsley, has become the first Brit to be killed in the fight against the violent terror group.
Last month, a 19-year-old soldier from the UK, based in Cyprus, was returned to his unit after joining the Kurdish peshmerga, telling family "these guys need our help".
And in December, it was reported that two former British soldiers had also joined the operation against Islamic State, saying they had been "compelled" to help after the murder of aid worker Alan Henning.
A 17-year-old male has become the second person to be arrested in connection with the murder of teenager Alan Cartwright, Scotland Yard said.
The 17-year-old was arrested on suspicion of murder this morning at an address in Camden. He remains in custody.
Alan, 15, was stabbed to death in Islington, north London while riding a bicycle with his friends
Police must either charge or release the two suspects in the Becky Watts murder investigation by this afternoon as time to question them further will run out.
Under UK law, suspects can only be held in custody for a maximum of 96 hours. A 28-year-old man and a 21-year-old woman were arrested on Saturday.
ITV News Correspondent Rupert Evelyn tweeted:
A former US soldier who said he fought next to an ex-Royal Marine reported to be killed while fighting with Kurdish forces against Islamic State militants has paid tribute to his former comrade.
Posting on Facebook, Jordan Matson said he was "honoured" to have fought next to Konstandions Erik Sculfield, praising his discipline and dedication.