So I emailed britpart and received prompt response.
"Hello Sam
Sorry to hear you have had an issue with this part, Can I please have the pictures of the parts, we will need them back for urgent inspection, as we have never in our history have a swivel shear in half, these are oem as per Land Rovers, if you can provide your full address, I will get a courier to collect them, Can you please send me details of your vehicle, as inspection will need to complete a returns form, and the company the parts were purchased from, as much detail will help."
So I emailed back the info and some pics and have left it with them.
Since further inspecting the ball I can see that it has a crack around the lower half of the narrow section, exactly where the previous one broke, so definitely well knackered this one.
Not quite sure how much my wheels are to blame seeing as these parts are probably unbreakable in theory, I'm thinking comp safari etc, how much stress is caused from a 10ft jump etc, I dunno.
Just a shame that they break for me really