Consultancy and computer programming services grew 4.4 per cent in the third quarter of this year, making them the single largest driver of UK GDP growth across 2026, according to the Office for National Statistics (ONS).

The figures, released by the ONS, show the wider UK economy expanded 0.7 per cent between July and October. Within that, the information and communications sector — the industry grouping that contains consultancy, software development and telecommunications — grew by 2.1 per cent in the quarter. Firms are buying advisory support to implement artificial intelligence and other technologies, and that spending is now visible in the national accounts.

What is behind the surge in consulting demand?

Tamzen Isacsson, chief executive of the Management Consultancies Association (MCA), the industry body for UK consultancies, said the figures "underline the important contribution consulting makes to the UK economy."

"Our latest insight and data from leading firms show strong growth in fee income of six per cent for this year as forecast," Isacsson said. Fee income (the revenue consultancies bill clients for their services) has therefore kept pace with the sector's official output growth.

She identified the engines of that growth precisely. "This is being driven in large part by client demand for digital transformation, AI and cyber security advisory services. AI in particular is a significant growth area, as organisations move beyond experimentation and look for practical support to deploy the technology effectively and deliver measurable benefits," Isacsson said.

Her account matches the experience of London-listed advisory group MHA. Dean Hughes, the firm's head of consulting and digital, said MHA is "seeing organisations across many sectors investing in technology, data, and AI solutions; and they are using advisers to help them do the implementations and manage the risks the tech brings."

Hughes added a concrete marker of demand: "This past quarter has been the busiest of the year for MHA's consulting and digital service line."

How did accountancy and legal revenues perform?

The consultancy boom coincided with a sharp rebound in two adjacent professional services sectors, both measured by the ONS monthly business survey.

Accounting industry revenues rose 13 per cent in September to £4.25bn, up from £3.75bn in August. August had marked the sector's lowest monthly figure so far this year.

Julie Matheson, accounting industry regulatory partner at law firm Kingsley Napley, put the swing in seasonal context. "August is, of course, always a quieter month due to the holiday season, but it is good to see that September's revenues bounced back amidst wider UK economic performance that was more positive than many expected," Matheson said.

She cautioned, however, that the outlook carries risks. With the "ongoing Iran situation, rising UK inflation and interest rates and the adoption of AI impacting business models, firm leaders would be advised to remain vigilant in their business planning," Matheson said.

The UK legal industry recorded the sharper jump of the two. Revenues spiked 15.5 per cent in September to £5.35bn, up from £4.63bn in August, according to the ONS monthly business survey.

What does this mean for the professional services outlook?

The third-quarter data confirms a structural shift in how UK businesses spend on external advice. Consultancy growth of 4.4 per cent outpaced both its parent sector, at 2.1 per cent, and the economy as a whole, at 0.7 per cent.

The MCA's own forecast of six per cent fee income growth for the year, supplied by its member firms, suggests the demand for AI deployment support — rather than experimentation — will keep the sector at the front of UK growth through the fourth quarter.