I have an enlarger lens which was made by Wray of London. It is marked as a 3¼in f/45 supar SER III.
The aperture setting is engraved in the sequence: 1, 2, 4, 8, 16, 32.
I’m interested to understand the aperture sequence, and why is the lens marked f45 when the setting only goes to 32, any ideas anyone?

Are you sure it isn't f:4.5?

Anyway, the settings are for relative exposure. 1 second at "1" equals 2 seconds at "2" and so on.

The Lens Collector's Vade Mecum, which tends to be good on British lenses, has this to say:
Series III These can be traced back to a f4.5/6in lens in B.J.A. 1955, p206, but may not have been in all foci
then. It was recomputed, so that it was optimized for the reproroduction ratios most used and will give
extremely good sharpness and colour correction for 5x4in negatives. It was in a black mount with bold white
iris ring to f32. These last were a rare earth glass design although this was not noted in 1955. Cost was
£15.50.
Supar 111 By 1955, these were Series 111 as follows:
f3.5 36, 50mm
f4.5 2, 3.25, 4.25in
The example noted in 1968 did not have a serial number on the front bezel.

I have a similar lens - close examination with a nuclear-powered loupe reveals a decimal point between the 4 and 5.
As Ole says, the markings are intended to indicate relative exposure requirements at the different apertures - if the markings are whole-stop steps starting at f4.5, the smallest will be f25.

You are right, there is a suggestion of a dot between the 4 & 5.
Thanks for that information; I was begining to think I had an f1 lens; but it looked a bit small for that. One fine day I shall make some prints with it since it seems to be in very good condition.