I am in desperate need to find an experienced doctor in subcision within the U.K. (North)

Dear Louise Maria, Thank you for your question.  In my own experience, subcision is not always the best treatment for improving acne scars.  It is a procedure that was popular some time ago but it is now known that it sometimes aggravate the dermis leading to even more scarring.  Treatments using laser energy are now considered the better treatment for acne scars.  I advise you to look for a CQC registered clinic in the North offering either C02 or Fraxel lasers and request a consultation to get their views on what is going to be better for you. I wish you well with your treatment.  Best wishes,  Dr Haus.

As above, I would not recommend anyone else, as Prof Chu is an expert, and has teaches this procedure to other dermatologists. 
Acne scar revision comprises of specialised procedures. For the best results, one should target the acne scar type with ideal treatments METHODS. Using one device is not optimal. As everyone has a unique pattern of acne scarring, the best solution is a tailored one.  The web reference below will take you to a resource to help you understand acne scar revision at a specialist level. I embedded all the videos in one page to help. 

As an example deep ice pick scars, and narrow box car scars are best treated with TCA CROSS. Deep narrow scars respond better to this treatment than even the most expensive lasers. On the flip side, rolling, and atrophic acne scars can improve with fractional devices such as Fraxel, fractional lasers, ProFractional erbium lasers, Infiini –Intensif –Intracel radiofrequency microneedling. Atrophic scars (depressions) can be treated with either fat grafts, PRP or dermal fillers. Tethered and anchored scars are best treated with surgical techniques such as subcision. Other surgical techniques that I use include punch elevation, surgical elevation, punch excision and traditional excision for focal scars. Early and very mild acne scars respond well to eMatrix and non-energy microneedling, as well as vascular lasers. Skin colour changes such as PIH or dark marks respond best to sun protection, creams, and Q switch lasers in the nano and pico pulse durations. 

The majority of patients will have a collection of different scar types, and hence a tailored treatment METHOD will be best. Careful examination, especially under angled lighting with scar mapping will give you an understanding of what are the best options for your scars. Additionally tactile examination namely touch will give me an understanding of the amount of subdermal fibrosis, as special equipment is needed for this sub-set of acne scars.  In the majority of patients its finding the correct combination that give you best results, and everyone is unique! It is never about the device, its about the specialist behind the equipment that will deliver the best outcomes. All the best, Dr Davin Lim. Acne scar dermatologist specialist. Brisbane, Australia.