Barclays is to start selling information about 13 million customers' spending habits to other companies, and has admitted it could share the data with government departments and MPs.

In letters being sent to customers, it is also outlining what details about them it holds and uses which, it said, "may include images of you or recordings of your voice", as well as comments made in interactions with the bank on social media sites such as Twitter and Facebook. Barclays said it may collect "location data derived from any mobile device details you have given us" - suggesting it will be able to pinpoint where in the world a customer is at a particular moment in time.

However, the bank assured customers that any data it passed on to third-party companies would be aggregated to show trends, and that individuals would not be identifiable from it. A spokeswoman said there was "nothing sinister" going on, and added that it would not be profiteering from customers. Like most companies, Barclays has previously used customer data internally, but it has not shared it with third parties before. It is writing to current and savings account customers to let them know about the changes, which will take effect on 9 October.

A leaflet details the "new ways" in which Barclays' companies can use customer data, stating: "We can combine information about you with information about other Barclays customers to create reports which we may share with companies outside Barclays. This information is numerical and not personal, and you will never be identifiable on the basis of it." This could include data on how much people spend on different products and services.

The bank said the data could be passed to government departments and MPs – for example, to give them an insight into what was happening in their constituency.

Hmm, so how can they be "not profiteering from customers" when they're selling the data? Do they not understand the concept of selling something?

Hmm, so how can they be "not profiteering from customers" when they're selling the data? Do they not understand the concept of selling something?

Very little that bank sells is actually real it seems... I'm gonna write a letter to my crappy outfit and ask them what they HAVE to hold on me, then ask them to delete the rest and confirm it.

Moving your account would probably be quicker and send a more substantial message.

That can be very hard for many. Look at how few people actually do.

Moving your account would probably be quicker and send a more substantial message.

Overdraft is a very common trap used by banks.