The HCPC regulates 16 health and care professions, from paramedics to speech therapists, hearing aid dispensers, radiographers, chiropodists and dietitians.
From August 1 they will also be responsible for regulating social workers, taking over from the General Social Care Council (GSCC).
And the organisation's name will change to the Health and Care Professions Council (HCPC) to reflect the diverse professions it regulates.
Dr van der Gaag, HCPC chair, says in the two years since the transfer of regulation was announced her organisation has undertaken a huge logistical task.
"First of all we arranged for the transfer of the register of 85,000 names and contact details of social workers registered with the GSCC.
"Then there are the preparations for taking over our education role, all the programmes which are running in the universities and colleges that train social workers.
"Plus the transfer of all of the existing fitness to practise cases, complaints that have been made and logged by the GSCC but are in the process of being completed. Those are big operational issues."
Dr van der Gaag also had to engage with the social workers themselves "on the ‘why', the ‘what' and the ‘how' of this transfer."
Neither the social work profession nor the HCPC had anticipated the transfer of regulation when it was announced in 2010.
"Initially it was a huge shock – it probably would be fair to say it came out of the blue they were not expecting it and neither were we," explains Dr van der Gaag, who along with her role at HCPC is a research speech and language therapist and Honorary Research Fellow in the Faculty of Medicine, University of Glasgow.
"There were some people who were fairly vocal about that policy and didn't particularly like it because they felt they were losing something. What we have tried to do over the last two years is demonstrate to them that they are actually gaining something from this transfer.
"When you have your own regulator, you see that as a much better arrangement than moving into a multi-profession regulator.
"As relationships have been established through the networks we have built up - we have been attending conferences and working with professional bodies, the unions and the employers - my sense is that reactions are becoming more positive, but it takes time for people to get used to this kind of change."
So what are the positives for social workers and the public they serve?
"The key things are standards, sanctions and powers," explains Dr van der Gaag.
HCPC will set standards under its legislation for not only the conduct of social workers and the other professions but also their competence, their knowledge and skills.
"The standards that we have been developing with the profession describe their competence as well as what is expected in terms of their ethical practice, their behaviour and conduct.
"The standards have been expanded and that can only be a good thing. Then there is continuing professional development - that will bring a much more outcome-focused approach."
The new HCPC will also have a wider range of sanctions that it can impose.
"If a complaint is made about somebody, the case is brought to a hearing and that panel of experts can put conditions of practise on a social worker which under the current system they cannot do.
"We have powers to demand information, which means the fitness to practise process can proceed more quickly and is not held up because people are not cooperating.
"If they do not cooperate it is a criminal offence."
Dr van der Gaag says that the HCPC's experience with the other 15 professions means there will be "a huge amount of crossover on standards, ethics, conduct and competence".
"There is the same process in terms of handling complaints whether you are a physio or a social worker.
"But when handling a complaint about a social worker, we always have a social worker on that panel, in collaboration with a lay person.
"It is key that we have lay and professional people working together in the regulation process.
"We have recruited over 80 social workers to work with us.
"We have over 700 partners drawn from the professions and they make the day to day decisions, decide who comes on the register, they go out and visit the educational programmes, sit on the panels and decide whether sanctions should be imposed on their fellow professionals."
And who regulates the regulators?
"We are accountable to the Council for Health Care Regulatory Excellence, soon to be renamed the Professional Standards Authority for Health and Social Care," Dr van der Gaag explains.
"They undertake performance review of all the health regulators - it is the regulator of regulators and has a very robust methodology for holding us to account."
Social work's image has suffered in recent years with the high-profile cases such as Baby P.
Dr van der Gaag thinks "more comprehensive standards, robust standards, enhanced powers to investigate" will enhance social work's standing.
"Making sure only those who are fit to practise are in practise can only strengthen the profession."