Since several posters have mentioned the possibility of strikes, here is a web site which is good for finding out the status of Tube and overground services: https://tfl.gov.uk/tube-dlr-overground/status/, and here is a site for the Heathrow Express: https://www.heathrowexpress.com/time...e-disruption#/

You can also sign up for email updates. The unions must provide notification of future strike dates, so you are unlikely to be surprised if you keep up with the status of services via the above sites.