Have you heard about ERNIE 1? It is the world's first random number generator machine to generate the winning numbers for Premium Bonds and operated using several valves and transistors on circuit boards. It was manufactured on 1957. It is a free entry special exhibit and you will learn many things about this machine and computing itself.
The future of food will be always a popular topic because over 1 billion people continue to live on the borders of hungriness. Will genetically changed food be a solution or nightmare for humanity? This exhibition is also in the format of discussion and duration is around 30 mins.
Without an IMAX 3D movie, a science tour never would be complete. Deep sea monsters, dinasours, bugs, sharks, human body and space station are some the most recommended IMAX science journey films.
I would also recommend checking online science museum stuff if you don't have a chance to visit London.