Background The most common obstacle to registration with a GP practice in the UK is difficulty presenting proof of address. NHS guidelines stipulate that inability to provide ID or proof of address is not reasonable grounds to refuse registration. Practices may ask patients to present ID/proof of address, but need a policy in case patients cannot. Aim To find out how many London GP practice websites ask for documentation without a policy for where this cannot be provided and compare how GP practice websites describe the registration process in patient-facing material. Design and setting Cross-sectional study of practices from 10 London boroughs (n = 100). Method A proforma was piloted and then implemented, recording whether practices ‘demanded’, ‘requested’, or ‘mentioned’ photo ID or proof of address and whether there was a plan for patients without documentation. Text relating to documentation from all 100 practices for registration was subjected to thematic analysis. Results Out of 100 practices 75% asked for documentation. The majority of these were ‘demanded’. A plan was included for people without documentation in 12% of practice websites. Five themes emerged from analysis of website content: reassuring people without documentation; diverse requirements between practices; conflating administration and treatment; withholding treatment; and immigration and ethnicity. Conclusion Many practice websites breached NHS Standard Operating Principles and possibly the Equalities Act 2010. All practices should create a clear policy for patients who do not have photo ID/proof of address (for example, including a named receptionist), and update their websites accordingly.