With the 2012 relocation of its headquarters to 400 Atlantic Street in Stamford, Conn., pictured, Charter Communications gave the city a major new Fortune 500 headquarters. Photo: Alexander Soule With Royal Bank of Scotland potentially leasing portions of its Stamford office building to other tenants amid massive layoffs at 600 Washington Blvd., pressure could increase on the owner of another big office building that now houses Charter Communications.