She said: “I remember my father had one, he used to get so cross when it didn’t scramble. Took some time to heat up and then work.”
A former Bletchley Park code-breaker was among the guests who attended the centenary celebration.
Ruth Bourne, 92, shared her experience of being a pivotal cog in the intelligence nerve centre in Milton Keynes, Buckinghamshire, during the Second World War.
She said: “I was operating the Turing Bombe machine, but I didn’t realise the enormity of the work we were doing – all we were told was that we were breaking German codes.
“We didn’t realise at the time how difficult it was going to be or that there were 159 million million million ways that one letter could be encrypted.
“The only thing we knew was that it was very important to be 100 per cent accurate. Perhaps I was clumsier than most, because I was told to be 150 per cent accurate!
“What the Germans didn’t know was that the code was being slowly broken.”
Also among the guests was the eldest grandson of GCHQ’s first head Alastair Denniston, as well as Alex Younger, chief of the Secret Intelligence Service (MI6) and known as “C”, and Andrew Parker, director general of MI5, the Secret Service.