UK financial services group Prudential is the frontrunner in the public auction to buy HSBC bank's head office in London's Canary Wharf, researchers at merchant bank Kempen & Co have claimed. The property was put on the market last February with a price tag of £800 mln (EUR 1.2 bn). Market watchers believe it could now fetch as much as £1 bn, becoming the most expensive office building in the UK. Other investors included in the final shortlist of bidders according to Kemp & Co are UK real estate investment manager Prupim, two US investment funds and a private Middle Eastern buyer. The auction is expected to be conclude this week.