Given the market significance of the report it's damn obvious that this would happen. They should have assumed that security via obscurity was simply not enough, and the OBR should have been taking active steps to ensure the data was only available at the correct time.
> Hedge-funds would want to get the file as soon as it would be available - I imagine someone set up a cron-job to try the URL every few minutes.
It's not even just hedge-funds that do this. This is something individual traders do frequently. This practise is common place because a small edge like this with the right strategy is all you need to make serious profits.
