Personal data is now as important a commodity as oil, a leading QC has said as he warns companies that they need to be up front on what they are using it for. Dean Armstrong QC, an expert in cyber law, said as it becomes possible to collect ever more data businesses will have to ensure that they tell their customers exactly what they are handing over and why. From the hive which is used to control heating to the personal digital assistants that are increasingly used in peoples homes more and more devices are connected in the internet of things, but at the same time there is a “pincer movement” of tighter regulations. Mr Armstrong, co-author of Cyber Security Law and Practice, said data is now a “commodity as important as oil” and how it is used is now one of the biggest single issues which can “make or break” a company and its reputation.–– ADVERTISEMENT ––”What we are all coming to understand is that data is such a source for use and abuse that everyone has got to be so much more concerned about how it is dealt with. The realisation that you can’t be careless with data is really coming to the fore,” he said. “Young people, whilst they are big users of Facebook and other social media platforms, generally understand that their data is actually important to them and people must not misuse it.”It has got intrinsic value and it’s a major resource now. If you have someone’s data you can become that person. You can have control over their bank you can have control over their email address.”Companies are the custodians of data and they must use it in a way that is proper.”The warning comes in the wake of the scandal over the harvesting of data from Facebook which was used by Cambridge Analytica. New GDPR rules, which came into force in earlier this year, also mean that companies face harsher penalties for misuse or breaches of personal data. Mr Armstrong said: “The hive which most people have in their homes which allows for remote control of heating and lighting through the thermostat can collect and analyse data and it can compare that.”Anything that you have in your house, if you have an Alexa that’s a device that collects and analyses data. You say play my favourite song and it knows what your favourite song is, it knows your shopping habits – it knows a lot more about you than you perhaps would want it to.” Research has shown that experts could even determine with 90 per cent accuracy what TV programme a person is watching based on the electrical signals coming from the home. Mr Armstrong, a barrister with The 36 Group chambers, said that any company involved with these devices would have to be “very careful” and make sure they have “specific consent”. He said: “The consumer has to understand, as a company I have to explain what I am going to do with your data and why I need it. If I use it for a whole different purpose then you have not really given consent.”Gone are the days when it was effectively ‘We are assuming your consent until we hear otherwise’.” Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.