By Lars Mucklejohn Fast fashion giant Shein is reportedly stepping up preparations for a blockbuster IPO on the London Stock Exchange following regulatory hurdles and pushback from lawmakers across the pond. The firm, which was founded in China but is now headquartered in Singapore, plans to update China’s securities regulator on the change of its listing venue from New York to London and file with the London Stock Exchange as soon as this month, a source told Reuters. Shein is said to have started engaging with the London-based teams of its financial and legal advisors to explore a listing in…