The Web will "transform the way the BCS works", by giving many more ways to reach and interact not only with members but also with the wider IT community, McMullen told the society's recent Branches Congress.
Membership has been growing steadily, after sticking at about 33,000 in the early 1990s, and is currently well over 39,000.
"We are seen as a spokesman for the sector," McMullen said. "We are now having dealings with the Government's e-envoy, among others.We are seen as a good, effective ally that can tap into the professional community quite quickly to give views."
The BCS Web programme, which is now gathering pace, plus the fast growing activity of the new Education, Engineering and Technology, and Management Forums, will increase this potential - and bring new opportunities and questions for traditional structures.
"In my professional life I have been involved in working groups across Europe and the US, and in some cases I have never met any of the other members," McMullen said. "So there is the question of what constitutes a BCS branch or specialist group in an era where time and space are circumvented by the Web."
McMullen pointed also to the BCS' other role, as a learned society.The recent formation of the UK Computing Research Committee and its place as a BCS expert panel, reporting to the Engineering and Technology Forum, was formal recognition of this role, he said. The committee has already taken an advisory role on research funding and other support with the Engineering and Physical Sciences Research Council.
McMullen said the take-up of BCS qualifications in particular had brought new financial stability that will enable the society to move forward with confidence.
A big growth in demand has been seen for the certificates and diplomas in specific IT career topics overseen by the society's Information Systems Examinations Board, and in the European computer driving licence IT skills qualification. The computer driving licence alone has had more than 300,000 UK candidates since its launch four years ago, and several large organisations have adopted it as standard.
McMullen said such success has enabled the BCS to bring in more professional staff. "My perception is that the BCS has moved from a situation where all activity is run by volunteers, with headquarters staff giving support, to professional headquarters staff who advise the volunteers rather than just serving them," he said.
McMullen stressed that the BCS' commercial success took nothing away from the fact that the society's main activity is that of a professional body based on members. He said, "It is this that gives us the credibility as the spokesman for the sector and in other activities."