The government has a track record of wanting to sell off its citizens' personal data without consent. Under care.data, they planned to sell access to "anonymised" medical records that included date of birth, postcode, gender and ethnicity. After a public outcry, these plans have been put on hold but the latest suggestions could see the sale of sensitive tax details to third parties, including private companies, researchers and public bodies. The claim that data will be 'anonymised' is impossible to fully guarantee.
Open Rights Groups is calling for the UK government to stop the sale of personal data to third parties unless it asks for explicit personal consent. You can sign the petition here
(Disclosure: I co-founded the Open Rights Group and serve as a volunteer on its advisory council)