Counter-pressure is just pressure applied against the body to try and minimise the sensation of pain. for example, its used in 'natural childbirth' to help manage labour pain - it's essentially just putting pressure on an area of discomfort or pain such as the lower back. A compression bandage applied to a swollen knee would be another example of counter pressure. Some trigger point type massage involves counter pressure - the therapist presses hard on a sore spot, gradually reducing the pressure and the underlying pain gradually fades away.

In the UK, you will nowadays need to refer to the Royal College of Physicians publication which provides the UK guidelines for diagnosis and treatment of CRPS. It was issued May 2012. Low dose Ketamine infusion gets nothing more than a passing mention but is still regarded as experimental and consequently the guidance advises that it should only be performed in a research setting. You would need to identify an individual clinician prepared to carry it out at a suitable centre (nothing is listed to give any hint as to where/whom) It may even be that you could only access this treatment option as part of formal clinical trial if/when someone decides to run one in the UK.