Firms and practitioners across the country were affected by the fault, which the company reported was due to a power cut at a data centre in London’s Docklands. It left agents unable to log in to the Government Gateway, while some were unable to access the site altogether preventing submissions and affecting tax compliance.

The outage ‘points to the risk of putting so much online and the systemic issues there might be in having so much of UK plc online,’ head of ICAEW’s IT faculty Richard Anning told CCH Daily.

‘If members are processing their data and working online on a cloud-enabled system and the system goes down, obviously they’re going to stop working. There’s an issue of lost time, and they need to think of other ways around this. Do they have alternative suppliers? Can they use mobiles? Are there other sorts of work they can get on with?’

The fault also hit several major banks’ online services including Barclays, HSBC and Santander, while BT’s service status pages showed subscribers across England, Wales, Scotland and Northern Ireland had been affected.

The incident raised concerns for some over the government’s Making Tax Digital project, which at the time of writing is due to be fully operational in April 2018, after a public beta test from April 2017.

 James Abbott of Abbott Moore and spokesman for the UK200Group said: ‘If that outage happened coming up to a quarterly deadline for filing on the Making Tax Digital portal, it would have been a real, real problem. If you file things late with HMRC and there’s a reasonable excuse, and the BT outage would have been a reasonable excuse, but the penalty would have been levied and you’d have to appeal against the penalty. That’s all time and something you’d have to do yourself or pay your accountant for.

‘In the broader scope of Making Tax Digital, it’s an incredibly short timescale to hope to get anything in place that’s workable.’