When Jack the Ripper runs out of the shop, Ron says that Jack the Ripper is run over by a 32 bus. The 32 bus runs from Edgware to Kilburn passing through Cricklewood where Gary lives, so therefore cannot pass the East End of London where Gary's shop is located.
When Gary enters Ducketts Passage in 1945 from the wrong end he travels from 1945 to 1888 and meets Jack the Ripper. When they both run back along the Passage to escape the chasing mob they should end up back in 1945 and not 1999.