It’s hailed as the one day in the year when members of the royal family come clean about their finances. At the end of June, the palace regularly opens up its books to public scrutiny when it publishes not just the report on how much the royal household has spent but also the financial results of the Duchy of Cornwall and the Crown Estate. In a year when the disclosure of the Queen’s and Prince Charles’s investments in offshore tax havens has been met with a deafening silence from their officials, a loosening of lips was long overdue.

There has been no word from the prince’s spokespeople on any plans to change how his foreign holdings are overseen

Thursday’s disclosures show that the Queen is doing very nicely from her taxpayer-funded sovereign grant, which rose to £76m last year and will go up to £82m in the current year. Some of this money is allocated for the refurbishment of Buckingham Palace, which will cost us all an eye-watering £369m over the next decade. Some of the costs could be clawed back if Buckingham Palace were opened up more to the paying public – as happens with the Swedish royal family’s palace in Stockholm, which welcomes visitors all year round. Yet the UK family has so far failed to do so.

Prince Charles is in the money, too. His income from his private estate, the Duchy of Cornwall, is expected to rise in 2017-18 to a record £22m. He also gets another £1m or so from the public purse to pay for his travel costs.

Transport has long been the royal family’s Achilles heel. A single visit last year by the Prince of Wales to India, Malaysia, Brunei and Singapore cost a staggering £362,000. It’s partly down to his air fare. The prince might need expensive, non-scheduled flights on RAF planes for security reasons, but costs could be kept down if he had a smaller entourage. For shorter trips, scheduled flights should be given greater consideration.

We also learned that he has increased the amount of his Duchy money going to William and Harry from £3.5m to £4.9m a year. Most of this sum (which also includes some capital spending) is allocated for their public duties, but because we are given no breakdown it is unclear how much is used for personal spending. And now Harry has a new bride, we still do not know how much extra money will go on expenditure for Meghan.

So far there has been no word from the prince’s spokespeople on whether, after the embarrassing revelations in the Paradise Papers about the Duchy of Cornwall’s offshore investments, there are any plans to change how his foreign holdings are overseen, or if they will be made more transparent.

There are two other odd things in Thursday’s announcements that work against proper scrutiny. First the choice of date. The announcement coincided with Prince William’s Middle East tour, which meant that most of the royal press pack were abroad rather than at Buckingham Palace and Clarence House – and were thus unable to cast an expert eye over the accounts. Was this deliberate? There were certainly mutterings from some royal correspondents that the announcement should have been rescheduled, although the palace maintained that the date could not be changed because the reports had to be passed to parliament.

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Second, there is the question of bringing out three financial reports on a single day. Reporters and analysts received a mountain of data, which had to be quickly processed. To cynical eyes, this looks like the palace managing the message: they take a single hit on a single day, rather than having a succession of bad press days.

To be fair, the palace is more forthcoming with its financial information than in the past, and this one day of openness is a step in the right direction. But wouldn’t it be healthier if this happened all year round?

• David McClure is the author of Royal Legacy