DPF removed and cleaned using by these guys - Blocked DPF Cleaning Service, the UKs fastest & most effective - UK DPF - who as I mentioned happen to be just a mile away from me. Total cost was £189 + VAT (£!49 clean, £40 removal and refit) which, given that it restores the DPF to as good as new and is a guaranteed job, I'm more than happy with.
Actual bill was higher as I had the car serviced as well as the last 3-4 services only seem to be oil/filter changes. Goes like a rocket now, and no errors whatsoever.