The advice comes as IT managers are under intense pressure from the board to use IT investment to cut costs or boost profits.
There is also scepticism among companies over whether the promises by outsourcing providers, such as a reduction in costs and improved efficiency, can ever be measured.
"There is a strong link between spending on IT and productivity if you link it to a general business redesign and re-skilling," said Thomas.
Although he expected the overall market for the UK services market to remain relatively flat over the next year, demand for business process outsourcing would continue to be strong, he added.
Many companies in financial services have already outsourced processes such as mortgage processing and cheque processing, in a bid to reduce costs in parts of the business that are not deemed a competitive advantage.