Passengers are being warned that the London Underground will be forced to close if two strikes planned by Tube drivers go ahead.Aslef, which represents about 2,000 Underground drivers, has called two 24-hour walkouts, on Thursday November 7 and Tuesday November 12.Transport for London says that if the strikes go ahead, “no London Underground services are expected to run” on Thursday and “severe disruption with little to no service is expected” the following Tuesday.