Contact Dr Martens direct for a list of recognised repairers.
I am a former shoe repairer. I was always advised to absolutely avoid trying to repair them due to the fact that this type of rubber was highly toxic when one attempted to repair it in the traditional manner repairers adopt.
With DM's the whole unit needs to be replaced and that requires specialist equipment, including a heat knife and the work needs to be done in a properly ventilated workshop.
Thank you! Looked on their website. ..Timpsons (Sainsburys car park) do them.
if i remember right there is a Dr Martens shop near camden station and they could help?