Update: Eurostar has updated its website and now has the latest details! Both a PCR test (max 72 hours before departure) and a rapid test (max 4 hours before departure) are required for travel to the Netherlands.
Eurostar recommends this clinic: https://www.privatecoronavirustests.com/page/how-does-the-test-work (clinic is 10 mins away by tube, with results in 15-20 minutes verbally and a certificate to arrive within an hour).
