Facebook has blocked attempts by the Admiral insurance company to adjust user's car insurance costs based on posts they publish on the social network.

The feature was designed to analyse the language used by Facebook users in posts, as well as check what they have 'liked' on the site in a bid to lower the cost of their car insurance. Admiral said the service, which was due to launch during the week beginning 1 November, would be entirely voluntary and would not look at photos or other content posted on Facebook.

But the feature was found to be in breach of section 3.15 of Facebook's Platform Policy, which states: "Don't use data obtained from Facebook to make decisions about eligibility, including whether to approve or reject an application or how much interest to charge on a loan."

The block is supported by the Open Rights Group, whose executive director Jim Killock said: "We need to think about the wider consequences of allowing companies to make decisions that affect us financially or otherwise, based on what we have said on social media."

'Thankfully Facebook pulled the plug on this shambles'

Admiral explained how the system would use an algorithm to determine how safe a driver might be based on the language they use in Facebook posts. For example, it claimed people who write lists and who arrange social events with friends at a specific time, rather than saying "tonight" are likely to receive a lower insurance quote. However, those who display over-confidence by using words like "always" or "never" instead of "maybe" are deemed a higher risk. The system would only offer discounts where available, the insurer said, and would not increase drivers' premiums.

Firstcarquote scans a "static snapshot" of a user's Facebook profile and, while it was said to focus on content produced in the last six months, older posts, likes and status updates could also be used to better understand the customer.

The insurer's actions have also raised legal concerns. Tom Jones, head of policy at campaigning law firm Thompsons Solicitors, said in a statement sent to IBTimes UK: "[Insurer's] repeated profiling of people is sadly unsurprising – this smacks of a captive market so arrogant it doesn't care about how it treats or is seen to treat its customers. Thankfully Facebook has quickly taken steps that the insurers couldn't see fit to do and pulled the plug on this shambles."

Admiral's system, called Firstcarquote, was aimed at new car-owners and younger drivers, but could be used by anyone.

Killock of the Open Rights Group added: "Young people may feel pushed into such schemes because of financial constraints. The right to keep things private shouldn't be the preserve of those who can afford it."

A Facebook spokesperson said: "We have made sure anyone using this app is protected by our guidelines and that no Facebook user data is used to assess their eligibility. Facebook accounts will only be used for login and verification purposes. Our understanding is that Admiral will then ask users who sign up to answer questions which will be used to assess their eligibility."

Admiral has not yet replied to an IBTimes UK request for comment.