On 15^th February 1951, a LEO diary note read: ‘It can be said that on this day, LEO performed its first programme before HRH Princess Elizabeth.’

LEO I was still under development at that time but later in 1951 LEO ran its first programme.

The Society Secretary wrote to the Queen earlier and received this reply a few days ago.

Ernest Lenaerts who was one of the designers of LEO I kept a detailed diary with technical notes and recordings of events left the following entry in his record of 16 February 1951
16-2-51 
HRH was no more and no less impressed than I had expected. The information printed by the Teleprinter was unintelligible except of course for the message printed at the bottom which provided some light relief. Fortunately LEO made few mistakes – obviously not subject to stage fright and the Demo went off smoothly. A little more interest was shown I think in the interior of the machine when she saw the complexity of the circuits – how many of this machines like these in existence?
Only one other in working condition – No others on commercial clerical problems. This auspicious occasion called for an enormous improve in general tidyness of the lab and I must make an effort to preserve this. My own desk was clear for the occasion – the first time in months. Work on the machine can go ahead again and I have been given a more or less free hand to proceed on which problem I deem the best tackled first. The object will be to bring the machine  to full operating condition as soon as possible so that Caminer & Co can get [[weaving]] on some of the programmes that they have kept up their sleeves for so long. The first and most obvious fault to be cleared is the corruption in the Teleprinter which I Think are due to breakthro in the output Unit. Other troubles to be cleared are occasional “1”s being added into the store. These have the effect of spoiling all of the test programmes received from Cambridge ”