Very good advice about sending in a meter reading a day after your DD has been taken, it works. DD seems to be worked out to first pay back a debt, then to cover your future annual bill based on last years consumption, so it can be high even going into summer. DD will always be more than needed in summer so send in monthly readings to make sure your account is accurate. Finally it is an option to pay quarterly cash and set up your own savings account to meet the bills, you are then in total control over how much you pay into savings each month. However some tariffs charge slightly more for quarterly cash, which demonstrates that the DD system favours the supplier.
A comment on the title of this topic, it is not possible to download smart data to your computer because the signals are encrypted. Many people keep useful spreadsheets of meter readings but they have to be made manually from regular readings.
Your last comment is misleading. Of course data can be downloaded, they have just chosen to not allow it at this time. Data will (should) be encrypted before it is transmitted to SP Servers. This is standard for any data transmitted by wire or wirelessly. It's time SP became far more transparent with our data and substantially improved their customer support. 45 min+ to talk to someone is NOT acceptable.
IHD displays are paired to the meters with a pass system set by the installer. Yes the data is there in your house but if suppliers allowed communication to your laptop there are obvious hacking dangers. The meters can accept a wide range of commands and communications can easily be two way. The smart program is therefore very protected not only by SP but all suppliers. People report data download in other countries and it would be interesting to know how this is safely achieved. Maybe the zigbee comms are completely separate from the 4G mobile phone comms? Whatever don’t hold your breath for any action on this.