I had the end of a rear spring on a Polo snap off and I have replaced it, but I didn’t get time to replace the other one. Going back in for retest tomorrow morning. I know its good practice to change both springs at the same time but will it fail the mot with just the one replaced? I’ve measured the wheelarch height on both sides and they are exactly the same.

No it won’t fail, that doesn’t even warrant an advisory.

Straight pass.