The Chancellor is set to this week outline the government's commitment to ensuring the ongoing "competitiveness" of banks.George Osborne is expected to on Wednesday use the annual Mansion House speech to pave the way for a review of the bank levy in a bid to prevent major lenders from moving their headquarters abroad.Senior industry sources contacted by the Sunday Times said a review was likely.The bank levy is a tax paid by the biggest lenders based and operating in the UK. In the March Budget speech, Osborne raised the levy from 0.156% to 0.21% of a bank's liabilities. It generates around £4bn for the government each year.The newspaper cited one source who said a review would have to postpone any plans to relocate until after it was completed, while a top five shareholder said it "could stop HSBC in its tracks".However, other factors are believed to be playing a big part in banks thinking of a move abroad, with one senior banker quoted by the publication as saying "it's not just the levy. It's the ring fence, the new regulations for senior managers - it's everything".One day ahead of Osborne's speech, HSBC is due to hold a meeting with its investors where he is expected to reveal the deciding factors on would keep its headquarters in the UK.