30th November 1951 - a momentous day!

16th November 2021

It was in November 1951 that the ‘electronic calculator’ that Lyons had been developing for some time actually started its working career after months of trials and experimental runs.

This made LEO the ‘world’s first business computer’.

Lenaerts notebook

That first successful business program was run in three parts, with P1 completed on Wednesday 28th November 1951, as Ernest Lenaerts records in his notebooks (above). The final part, P3, was completed by 2:35pm on Friday 30th, and in typically understated and factual style, Thomas Raymond Thompson (TRT) reported that fact to his managers in a memo (below) the following week.

1951 Lyons Memo

I thought it might be interesting to have a quick look at what else happened that year in the UK. This may provoke nostalgia, surprise, incredulity - but it certainly sets the context for the remarkable achievement that was taking place at Cadby Hall. 

So - to go through the year picking just a selection of milestones...

  • On New Year’s Day, ‘The Archers’ starts on the BBC Light Programme and also in January the UN headquarters building opens in Manhattan, New York. 
  • In February, the first transatlantic flight without the need for refuelling takes place.
  • In March, Dennis the Menace first appears in ‘The Beano,’ and in April the first UK National Park – the Peak District – is founded – followed later in the year by the Lake District, Snowdonia and Dartmoor.
  • May sees the Festival of Britain (below) opened by King George VI – timed to coincide with the centenary of The Great Exhibition. Burgess and Maclean defect to the USSR. The Goon Show starts. 
  • In June, GCE Ordinary and Advanced level exams are introduced, replacing the old School Certificate and Higher School Certificate.
  • It was a good year for films – in July, Disney’s cartoon ‘Alice in Wonderland’ comes to the UK and In August, Elizabeth Taylor stars in ‘A Place in the Sun.’
  • In September, Prime Minister Clement Attlee opens Europe’s largest oil refinery at Fawley on Southampton Water – but in October, Labour loses the General Election - and Winston Churchill returns as PM. Zebra Crossings are introduced – the first one in Slough.
  • In December, in the US, electricity was generated by nuclear power for first time. To finish this round-up, the film ‘The African Queen’ was released and John Wyndham’s sci-fi novel ‘The Day of the Triffids’ published.

Festival of Britain

Meanwhile....Over in Cadby Hall, Lyons' headquarters, work was going on throughout the year to prepare LEO for its future tasks. 1951 was a critical time, with trials and tests taking place regularly and modifications being made by the working team of engineers and systems analysts – led by John Pinkerton and David Caminer (click on the photos below to find out who's who).

Caminer and others


Ernest Lenaerts

  • In January, John Simmons, the man in charge of running Lyons’ huge clerical back office and who had led the search for new methods of carrying out the millions of daily transactions was promoted to the Board of the company.  
  • By February, LEO received its first VIP visitor – HRH Princess Elizabeth, who witnessed a trial run. It is gratifying to know that 70 years on, The Queen wrote to the Society that she ‘fondly remembers her tour of Cadby Hall and viewing Lyons Electronic Office.’ 
  • The small LEO team worked extraordinarily hard and by April they were ready to give a demonstration to the Directors of the company – who were obviously looking for a good return on the money they had invested in the project.
  • In May, Geoffrey Salmon, one of the directors and a member of the Salmon and Gluckstein family which owned and ran the company hosted a dinner at The Trocodero restaurant in Piccadilly ‘To celebrate the successful demonstration of clerical work performed by the calculator of LEO.’ The menu cover showed a blue LEO cabinet. 
  • Obviously there were the inevitable technical setbacks along the way – in particular with the equipment commissioned from Standard Telephone Company (STC) which in the end turned out not to be suitable. So, although initially the idea had been to start LEO on payroll straight away, this was later modified to start with an ‘easier’, though still important task  –that of Bakery Valuations. That month, a series of further demonstrations of how LEO would operate were given to managers around the company. 
  • By September, LEO was managing to carry out test runs with increasing accuracy and by mid-November it was almost ready to go live. Unfortunately, persistent ‘machine faults’ meant that the planned launch had to be moved forward.
  • At last, in the very last week of November 1951, the program did indeed go live and a note from TRT (TR Thompson) tells us that the ‘Cadby Hall Bakery Job’ was completed by 2.35 p.m. on Friday 30th – and that it ran regularly from that time onwards. Success! 

The news of this achievement spread rapidly – and before the end of the year, LEO was being used not just for Lyons tasks, but also for the Met. Office


As you will know, LEO has been acknowledged as ‘The World’s first business computer’ by Guinness World Records. The 70th anniversary of LEO’s very first ‘live’ run is an occasion we, the project team, are very happy to celebrate.

We're due to launch a new film about LEO to coincide with the anniversary - watch this space!

Posted by: Hilary Caminer




Photograph of 30th November 1951 - a momentous day! Click for a larger version


Help support the museum by buying from the museum shop

View all items

Founding Sponsors
redgate Google ARM Real VNC Microsoft Research
Heritage Lottery Funded
Heritage Lottery Fund
Accredited Museum