Under UK law, you have the right to see your statutory credit report for free from each of the three agencies. You can request these directly from their websites (e.g., the Experian Statutory Report).
If you check your report and find it’s looking a bit bare or lower than you'd like, try these immediate steps: Why you shouldn't worry too much about your credit score
Several third-party platforms provide free, ongoing access to your credit data by partnering with the CRAs: