He recently visited the firm's modern offices and met its 15-strong team. When he sold the business after six years, it handled 1,200 payslips a month.
Today, Dataplan has more than 600 clients nationwide, processing 35,000 payslips a month, paying more than £1bn in wages a year.
"I was delighted to see how the company has developed as the technology has improved, particularly in relation to communication," said Mr Allen.
"It means Dataplan can operate payrolls, whether they are in London or Scotland, by using the internet."
"What I was also delighted about was how the company has prospered over the years."
"It has a good, professional team which, from its base in the provinces, can compete favourably with agencies in, say, the south east, because it is a lower cost operation."
All has changed to when he first started the business, inspired by a pioneer in Peterborough.
"He was going around firms and picking up time cards. He had a large house full of ladies operating punch card machines," Mr Allen said.
"He then took them to a big computer which produced the pay slips. There were computers around in those days but it was still a novel idea, having an agency sorting out salaries."
"Now the atmosphere has changed. People have accepted this to be normal practice and not have a wages department working out tax every week."
"There were also, of course, no credit transfers in those days. People would mainly be paid in cash, and sometimes a cheque."
Dataplan managing director Richard Rowell was pleased to show Mr Allen around the firm and thanked him for his comments about the modern-day Dataplan.
"He showed great foresight to start in business with what was, a ground-breaking concept," said Mr Rowell.
"From those small origins, technology has allowed Dataplan to grow into a huge operation, handling payrolls for businesses and organisations such as schools. We have clients as far afield as Aberdeen and Cornwall."
"The last few years have seen particularly strong growth and our reputation, built on a customer-focused approach, was enhanced further when we were named best outsourced payroll provider by the Institute of Payroll Professionals last year."
"Forty years is a significant milestone for any business and it has been nice to celebrate that with the man who made it possible."
"As we have demonstrated, our success has been achieved by continually looking ahead and growing the business."