Whichever way you cut it audit remains one of the most lucrative parts of the accountancy business. Take the figures this year. Overall, the Top 50 firms are making an estimated £300m more this year than in 2006 from audit and assurance work. That means audit makes around 38% of total revenues, the largest contributor by a long way.

On a firm by firm basis audit was up an average 12.2%, a solid double figure performer that leaves no one in any doubt why the firms remain wedded to it as a service line.

Of course, audit assurance had received a massive boost in previous years when advice on the implementation of IFRS and Sarbox had been bundled in to audit revenues.

Those issues have receded as real drivers so the firms have had to find other ways – though without a burning issue to rely upon.

Richard Sexton, head of assurance at PricewaterhouseCoopers, believes the UK audit market is being driven, at the top end at least, by London’s position as the capital market of choice for overseas companies, the continuing entrepreneurial nature of UK business and the growth of smaller companies, plus the high level of activity in the private equity market.

There are other factors too. ‘We see increasing opportunities through the creation of public trust in non-financial assurance.

The final piece is the overall high level of deal activity and the assurance work needed for that,’ Sexton says.

Tax remains a lucrative field too making up roughly 26% or around £2.3bn of the combined revenues. Average rise was 14.7%, which contradicts the doom mongers who feared that tax would be badly damaged as a service line by HMRC’s disclosure regime.

The fact is that revenues are now focused less on avoidance and more on compliance advice with a few notable drivers including the continuing complexity of the corporate and personal tax system.

Oddly the US has added to this burden with the introduction of FIN 48, a new standard that demands the disclosure of ‘uncertain’ tax positions.

The European Court of Justice has made its contribution. Big cases on controlled foreign companies, overseas dividends and foreign losses has seen demand for expert advice as companies battle to overturn UK tax rulings.

But perhaps one of the most interesting service lines is corporate finance, which is now worth £1bn for the Top 50 firms. A little more than one in every £10 across the UK’s biggest firms is now earned from corporate finance, making it an essential part of the offering.

One of the exceptional performances was BDO Stoy Hayward with a 29% improvement, the highest among the top six firms.

Stephen Bourne, national head of corporate finance at BDO, said it was a success built over four years and based on careful recruitment and a very clear market focus.

Private equity, a good deal list for smaller public companies and PFI work have contributed to the department’s rapid growth at the firm.

How the sectors compare

Audit revenues have continued their upward trajectory. This year, the UK’s Top 50 firms reported a combined audit income of £3.3bn,up from£2.9bn in 2006 and representing an impressive 38.19% of total fee income.

The Big Four generated the lion’s share of audit fees (£2.5bn) but their growth rates in audit proved a mixed bag: ranging from E&Y’s 23%to a very disappointing 2% from KPMG. PricewaterhouseCoopers remains the biggest auditor with total audit fees of £952m, up 11% on 2006.