The Justice Sub-Committee's report, Brexit: acquired rights, concerns EU citizenship rights. These are fundamental rights under EU law to live, work, study, and raise a family in an EU Member State of one’s own choosing.
There was much talk before the referendum that these rights would somehow be protected as "acquired rights". This was misleading. If the UK wants to preserve certain EU rights on withdrawal, it will have to ensure they are safeguarded in the withdrawal agreement.
The majority of the safeguarded rights are likely to be reciprocal with EU rights. The report recommends that a mechanism be established to ensure that UK law can take account of relevant developments in EU law, and, importantly, that EU law can take account of relevant developments in UK law.