Thanks for the reply. Yes, the bottom bracket is square taper as I replaced it a while back.

I have found what I believe to be the correct SR Suntour set and then found a link to a better quality SRAM one, which I subsequently ordered.

I imagine I’ll have to re-index the gears after changing it.

I’ve watched a few YouTube videos on this and it seems quite simple to do if you have a crank puller. I reckon the gear indexing will take longer to do afterwards!