I am on FTTC with DLM always running, could I see a reduction in errors if I placed my router into a power surge protector?
If by power surge protector you mean mains conditioner, then I think it's worth a try. I plugged my Xyxel bridge and router into one of those Tacima things on the 10th August. Interleaving was taken off my line nearly 29 days ago; DLM had been "interfering" with my line ever since I moved from ADSL to VDSL more than 10 years ago. I still only get around 57Mb downstream on an 80/20 service though...
What's the evidence that the improvement was due to your power surge protector? The improvement could have been due to other factors. Easily.
Actually there's no proper reason why a mains conditioner would affect DLM anyway, unless BT have started using Tacimas to clean up their power supply...