@Laura @fellmoon don't go to Bletchley Park - unfortunately it's pretty much just a stately home these days with a few video screens to watch. Extremely disappointing!
All the good stuff (the colossus rebuild, the bombe, the harwell witch etc and rooms and rooms of old computers) is next door at tnmoc
Same carpark, separate (cheaper!) entrance/ticket
They used to be a combined entrance, but split about 10-15 years ago when bletchley also kicked out the model railway and cinema collections :(
@fellmoon brighton seems a bit out of the way for that route?
https://amberleymuseum.co.uk is near brighton and recommended if you like transport, phone exchanges, HV electricity things etc.
Bletchley is more directly between eastnor/harwich - but don't listen to anyone who tells you to go to Bletchley Park - all the cool stuff is next door at https://tnmoc.org (same carpark, separate entrance fee)
https://miltonkeynesmuseum.org.uk is near tnmoc too, and has a lot of geeky stuff to see