According to https://www.royalparks.org.uk/__data/assets/pdf_file/0010/65395/160812_CPB_cycle-policy-TRP-2016-approved_es.pdf (Cycling in the Royal Parks Policy Statement 2016)
Speed limits do not apply to cyclists within the parks but it is recommended that cyclists keep to appropriate speeds for the environment
I guess that came out after this
https://www.standard.co.uk/news/london/london-cyclist-fined-for-speeding-in-richmond-park-after-he-is-clocked-at-38mph-a3102191.html
@PhilDAS started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
According to https://www.royalparks.org.uk/__data/assets/pdf_file/0010/65395/160812_CPB_cycle-policy-TRP-2016-approved_es.pdf (Cycling in the Royal Parks Policy Statement 2016)