- Gary can only time-travel to or from a period when he is alive in his own time. That's why the portal reopened when he was born in 1962. When it closed in 1945 in "Accentuate the Positive", it wasn't because he saved Attlee; it was because the older him in 1999 died.
- Disproven by the sequel episode, "Many Happy Returns".
- Gary is actually the reason for Yvonne's great success as an entrepreneur. Although he is stuck in the past he knows the future, to bet on England winning the World Cup in 1966, to invest in oil before the energy crisis in the '70s, etc. He therefore amasses a huge fortune by the '90s and uses it to help Yvonne succeed with her business.
Gary theorised that saving Clement Attlee’s life was the reason the portal closed on him. Yet in the original timeline before he fixed his son’s life, it seemed it had stayed open. We can assume Gary did save Attlee’s life in the original timeline, since Gary’s memories didn’t change when he changed the timeline and he remembered Attlee being alive. So then why didn’t the portal close in the original timeline?It's possible that he was supposed to accomplish several things in the past, not just one. It’s possible that many of the things Gary did throughout the show such as letting Reg know his son, warning the Americans about Pearl Harbor, his mission to France, even having his son, were things he was supposed to do in the past. Maybe in the timeline where his son was a failure, he failed to accomplish one of more of the things he had to do and that’s why the portal never closed.
