Before I go out and part with my money, I am wondering whether 1/72-scale locomotive kits will fit the standard 'OO' track. The one I am particularly interested in is the 'WR360 C12' from Hobby Boss.

It depends.
If they have made the kit 'true to scale' the standard 00-track would be too narrow.
Brief history:
The British designed the 00-scale to be 1/72- To overcome the problems with fitting axle bearings and stuff beneath the carriages they designed the track width to be less than true to scale, the inside width of the tracks is actually at 1/87th.
When the Germans started to make msmall scale model railroads they used the 00-track and let made the rolling stock so that it would be the right scale for the 00-track (i.e. 1/87th)
and started calling it H0 (stands for Half-Zero since they considered it to be half the scale of the 0-gauge).

The tracks we can buy are therefore H0/00 and fits both the 1/87 and 1/72 rolling stock. I think british rolling stock is narrower so with the difference in scale they come out the same physical width.

Going strictly by the scale factors the inside width of the model rail track should differ by 3.4 mm between 00 and H0.

Looking at the underside of the kit (Google image search) I would say that changing the track width (assuming it is not H0/00-gauge) could become difficult.
I would either use the included track section or make my own true-to-scale track.

I found this image:
https://www.super-hobby.se/zdjecia/6/2/7/2701_1_HBB82913_1.jpg



which looks as if the track width is wider than true 1/72.
Even if there is something wronq with the picture I would still guess that the kit has a wider track width than 00/H0-track.
00/H0 should be 16.5 mm wide between the insides of the rails ...
/ Robin

Edit: See corrections of basic facts below

Um - a few corrections are needed. British 00-guage is actually 1:76, not 1:72. And it was designed to use the popular "half-0" guage that scaled out to 1:87 because track was available. But a combo of desiring an imperial scale and needing more width in the body for early electric motors meant they couldn't just go with 1:87 because UK trains are designed to an 8-foot width whereas US trains are designed to 10-foot width, giving more room inside a 1:87 shell.

But getting back to the original question, a 1:72 model won't fit on what is essentially 1:87 track. You could narrow the wheel spacing on the axles with a little creative surgery, but then you risk the loco looking a bit pigeon-toed.