Bluebutton Properties, the joint venture of Land Securities and Blackstone Group is to refurbish the RBS building in Bishopsgate, near London's Liverpool Street Station.Refurbishment of the 142,000 square foot building is expected to start in summer 2011 with a total cost of around £35m.Property group Land Securities said a planning application for the scheme will be submitted this month. RBS (Royal Bank of Scotland) has agreed to extend its lease, which expired in August 2010, until March 2011. The building was formerly let to Dutch bank ABN Amro, the company which RBS, led at the time by Sir Fred Goodwin, took over after a bid battle with Barclays.