You can always cut it at a certain height which will allow multiple offsets to emerge and eventually branch out.. Schefflera'S are often one of the indestructible plants so it shouldn't affect it negatively.
However I'd wait until spring to do any cutting/pruning.

You can use the bit(s) you cut off as (a) cutting(s). They root easily. In their natural habitat these plants can be quite vine-like so they do tend to have just one long stem unless you cut them back.

Cutting the plant back just before it enters its most robust period of growth speeds things along and is easiest on the plant. If you line in the northern hemisphere, that would be in mid-Jun.

If you've never repotted, you might consider planning a sequential repotting into a soil that allows you to water correctly, followed by pruning 2-3 weeks later. With that done, I think you'll be startled by the cooperation the plant offers for your efforts.

If you'd like to flesh out a plan, let me know and I'll help.

Al

I'm in the UK so yes, NH.

I put it into a nicer and larger pot a little while after I bought the young plant in which it has remained.

It seems to have regular growth spurts throughout the year, with more leaves growing from the top, it's going through another spurt right now, it seems.

A plan would be great, any help would be most gratefully received.

Thanks!