The congestion charge runs 7am – 6pm so I made sure I got to highgate before that so I was through it before it started. I got to highgate at 6.45 and car park was empty but I hear it fills up v quickly. I did manage to check in early and be taken to my room tho and was first in theatre so I didn’t have much waiting around for being too early. If you do have to drive through the zone it’s £10 paid on the day or in advance x