Hey & welcome! Often beginners do have these sort of problems that get worked out naturally with enough practice.

Originally Posted by: martyn5

I hope that with practice, I can manage to get my fingertips over and between the strings without comprimising the sound of the neighbouring strings. Is this usual for a newbie, or have I bought a guitar with too narrow a neck?

First let's review the mechanics of fingering chords for possible problem areas.

1. Fingertips to the last knuckle should be as straight down into the string as possible, as close to perpendicular to the fretboard as possible.

2. Press only as hard as necessary to get the note to sound. Any more is wasted effort and can make your fingertip skin spread out and mute adjacent strings.

3. Thumb behind neck and rest of hand and finger totally curled around to the front side of neck for best access to strings. Do NOT put your palm on the neck (big beginner issue that is overlooked).

4. Wrist and arm in a smooth natural curve.

As long as those basics are not at issue, we have to consider the machine. It's possible that your guitar does have string spacing that is too small for your fingers.

I have seen cases in which it is physically impossible (or at least impractical) to expect fingers (or hands) that are too large (or small) to play certain things.

So, before you just go on practicing thinking that it will get better, try this. Go to the nearest music store (or store that sells a variety of guitars). Play a bunch of guitars. Try to play some open chords & simple scales on lots of different guitars. Explain your issue to a salesperson. It may be that you need to buy and use an instrument that has wider string spacing. See if that fixes any issues right away.

Typically acoustic guitars, in particular classical nylon string guitars have larger than average string spacing.

Best of success with it. Let me know how it goes!