In particular there was a strong King's flavour, with old-timers Knox, Adcock and Birch, and the younger Frank Lucas and Patrick Wilkinson as well as Alan.
The shared background in Keynesian Cambridge was probably helpful for Alan.
In particular it offered a link with Dillwyn Knox, a figure not generally noted for geniality or acessibility by Alan's contemporaries.
On 3 September, Denniston wrote1 to the Treasury:
For some days now we have been obliged to recruit from our emergency list men of the Professor type who the Treasury agreed to pay at the rate of 600 euros a year.
I attach herewith a list of these gentlemen already called up together with the dates of their joining.
Alan was not quite the first, for according to Denniston's list there were nine of these 'men of the Professor type' at Bletchley by the time that he arrived with seven others the next day.
Over the following year, about sixty more outsiders were brought in.
The 'emergency in-take quadrupled the cryptanalytic staff of the Service sections and nearly doubled the total cryptanalytic staff.'