I presume they are copies of the US maker Pyro's 'dimestore' vehicles and figures; as the later Merit jeep was a copy, and this set seems to be a Bell offering, the earlier brand of Randall, parent of Merit.
One or two of the vehicles were marked BELL, the big red gun (shells/bullets missing? Certainly missing for the smaller piece) had 'A BELL TOY' while another just had a partial 'MADE IN ENGLAND' and with no label remaining on the box, it's hard to call whether they are copies or licensed/mould-swap types.
Certainly, as Merit, the gun would reappear [link]**, but with a metal axle and wooden wheels rather than the heat-welded stub-axles used here. The figures have been issued by several companies over the years and we will return to them one day, but as seen here always flat and - in this case - only the single figures present; the stretcher team and mounted officer of the original set not included/copied.
The tractor is in the US-specific 'row-crop' configuration with the front wheels brought together to make an almost tricycle undercarriage arrangement, as far as I know such a layout was never used in the UK. So not the most useful artillery-tractor either, with its agricultural-specific wheel set-up, but, hey, they were toys!
A couple of the marks and the machine-gunner; clearly designed as a gift-set with the red boxing, wouldn't you have loved to find this under the tree at Christmas? Did you get one? If you did you're older than me!
** The red 'link's - should you ever encouter another - are supposed to be note to me reminding me to add the link when I'm uploading the post at the library (then I remove the red text!), in this instance I can't find the bloody post?!! I'm sure I have posted both the gun and the box, seperately, but I might be getting confused with the Jeep/gun combination, so I will dig it (the gun) out this weekend and post it for Tuesday . . . if I have it here? Doh!