Last week, Accountancy Age reported that the UK’s largest accountancy firms are about to switch to online filing of SA returns and noted that e-filing has to date been driven by smaller firms. This begs the question: why have they only now – ten years after the first SA return was e-filed – decided to move to electronic filing?

The introduction of a tighter deadline for paper returns in 2008 (31 October as against 31 January) is obviously a factor. It is difficult if not impossible to obtain all of the necessary information by 31 October for someone with partnership, trust or overseas income, or who has very complex affairs. That makes the extra three months available to those who e-file very attractive.

But there have been specific barriers to e-filing. Returns for taxpayers with complex affairs need significant supplementary information and the facility to attach up to 5Mb of such information in PDF format was only added in November 2006.

There have also been concerns over HMRC’s ability to handle large volumes of electronic returns - especially at peak times - and large firms generally have more authorisation and control issues than smaller firms.

The need to cope with peak volume was stressed by Lord Carter and with much improved IT infrastructure the SA system worked well this year, with almost three million returns filed on-line. The second issue was eased to some degree when it became possible to file a return without a 64-8.

So, if 2008 is likely to see another very significant hike in the number of e-filed returns, most with substantial PDF files attached, will HMRC’s IT systems cope?

The key is the Carter Principle: that no new service will be launched unless it has been fully tested. Because the profession has repeated this like a mantra for the last year, HMRC’s Carter Project Team have made it a core principle. It explains why they have put back the implementation dates for the PAYE, VAT and CT elements of the Carter timetable. The idea that it is better to get one thing right at a time seems to have been accepted.

That is a major step forward and makes now the right time for the larger firms to come aboard.

Speaking for a firm that has e-filed for a decade, I think they will find that once everything is up and running it will turn out to be a good move.

Paul Aplin is deputy chairman of the ICAEW Tax Faculty and a tax partner with A C Mole & Sons