So today my wife goes to the British consulate to get a vistors visa for the UK and they screwed up and did one in her maiden name and then she showed them that it was wrong and so they put a big red cross thru it and wrote above it in pen. "Cancelled without prejudice"

Now, the problem I have with this is one. They burned a page in her passport due to their own incompetence. ie. the name on the visa didn't match the application. They simply took her name in her passport and didn't see the name change page.

Secondly, a red cross on any page in the passport is not a good thing and secondly there's nothing official about the Cancelled without prejudice. Anybody could have done this themselves and I'm afraid an immigration officer is going to act indifferent because of this or this would affect any future visas she goes for.

Are my concerns warranted or am I over-reacting?

Believe you are over reacting but it does point out the fact the old passport name change is not a good idea. A new passport in the new name only costs about 1,000 baht.

' WITHOUT PREJUDICE ' means exactly what it says. Cancelled or voided without prejudice....ie administratively cancelled only. ALL diplomatic posts know that means without any probblem.

Two of my children have Thai visas in their passports that were cancelled without predjudice due to an error with the issuing consulate. No immigration officer or embassy official has ever batted an eyelash at them. Should be fine.

What you don't say , but is probable , is that they cancelled the first visa and

replaced it with another.

This happened to a TGF where they issued a 1 month Schengen and then

replaced it with a 3 month.

Happened to me (current passport) where a single entry was replaced by

a double entry.

If you get an immigration officer who can't understand the obvious just

look along the line for one that isn't dribbling.