If the launch takes place as currently planned (April 1, 22:24 UTC) we may be able to see the Trans-Lunar Injection Burn from the UK 25 hours 37 minutes later so around 2026-04-03 00:01 UTC although the spacecraft will be low above the SW horizon. An ephemeris is available from JPL Horizons.
From Chelmsford the spacecraft rises around 23:49 on April 2 and at the time of TLI it will be 10 deg up at an azimuth of 209 deg.
Almost 60 years ago, on 1968 December 21, Chris Taylor saw the Apollo 8 TLI from Chelmsford. There is a really good S&T write-up here:
https://skyandtelescope.org/stargazing-and-observing/stargazers-corner/apollo-8-view/
I would like to reproduce that observation!