London, UK is not in the Schengen area hence flights from ZRH to London will depart from one of the non-Schengen areas of the airport (D or E gates). The E gates are located in a separate concourse that requires a train to reach. You have to pass immigration control to board the train. I am not sure why you want to go back to the A (Schengen) gate area after exiting and reaching the E gates as you can reach any non-Schengen departure gate from E without re-entering Schengen, but presuming you hold a passport which allows entry to Switzerland I don't imagine you would be denied.

I would suggest reviewing a map of the ZRH airport, all the details can be found on their official website.

https://www.zurich-airport.com/passe...-en/site-plans