As there's a risk of you receiving out of date information here, I'll try to clarify the position.
Under the provisions of the Data Protection Act 1998, you were entitled to be given any information held about you by almost any organisation, with just a few fairly obvious exceptions (such as that held by the police or security services relating to active enquiries). However organisations were entitled to make a charge for providing such information. The maximum fee (which was nearly always charged) in most cases was £10 but for medical records it was £50.
Then the EU's General Data Protection Regulation (GDPR) came into effect. (It remains in effect, even though the UK has left the EU, by virtue of the provisions of Data Protection Act 2018, which replaced the 1998 Act). The GDPR strengthened the old Data Protection Act and removed the ability of organisations to charge fees for providing data other than in very limited circumstances (such as when an individual makes a repeat request, after having already having been provided with the data, or when a request is manifestly unfounded or excessive). So you can now access your medical records free of charge.
This information, from the Information Commissioner, is aimed at health care providers (rather than being directed towards patients) but it explains the situation well anyway:
https://ico.org.uk/for-organisations/guide-to-data-protection/guide-to-the-general-data-protection-regulation-gdpr/right-of-access/health-data/