Factual error: Liverpool Street Station is shown as more or less deserted in the hours of daylight. The only way this could be achieved in real life is by phoning in a bomb threat.
Visible crew/equipment: When Ethan is going down to the security room on a rope you can see a man standing on the floor at the bottom. It's right after he starts to descend.
Suggested correction: What Sacha said is correct, but if this is referring to the second time Ethan descends into the room, then... that's obviously the employee that entered the room, not a crew member.
Factual error: In the scene of the eurotunnel train the ticket collector is wearing a 70s British Rail uniform This was the national railway company for Great Britain but is now defunct due to privatisation in the 90s.
Suggested correction: At the time of filming, British Rail would still have existed as it was only being dismantled in the mid 90s. However, I think Eurostar would provide their staff with different uniforms.
Plot hole: In the famous raid on the computer room raid, where Hunt is lowered from the ceiling, we see a close up of the screws to the vent being undone and caught in a holder so they don't fall on the floor. But the screws cannot be put back in their holes and done up once the vent is closed, and there is not enough time for Hunt to be pulled back up and the vent closed and screws replaced when the operator returns to the room, as Hunt was pulled back up with seconds to spare.
Suggested correction: They would not have to use screws to reattach it. They could use tape, glue, or magnets.
Suggested correction: It's night. After Ethan sees that his parents have been arrested, he walks out in the streets, and it's dark outside. Several shots later the big clock in the station is shown, and you can see that it's about 11pm.
This validates the entry rather than correcting it. If it is 11.00 pm the pubs have just closed and Liverpool Street Station would be heaving. This is true of any mainline station in London - as well as the fast food restaurants associated with them. Any Londoner knows that.