Among other things, I currently get to grade essays.
I hate the phrase 'in fact'. Usually what this means is that the student hasn't got any back up for their argument and has decided to say it's a fact in the hope that I won't question it.

Everything in their essay should already be a fact, so I wonder if I should then put crosses everywhere that they haven't written 'in fact' on the basis that those claims clearly aren't as factual?
( Matazone has new icons, but is keeping this one, Mon 8 Oct 2012, 16:40, 4 replies)

It's a valid expression when you're contrasting a previous claim or situation mentioned that was false or the reverse of expectations.

The coalition forces expected an easy victory and to impose their will on Iraq. In fact, the post-invasion period was a decade of continued conflict.
( cumquat may will not be commenting further on the allegations, Mon 8 Oct 2012, 17:22, closed)

In colliquial language, yes,
but the tone would be more formal with the use of 'however' instead. I'm sure the BBC write like that, but they currently seem to have a campaign to encourage one-sentence paragraphs, so I'm not going to hold them up as a standard of formal written English.

The coalition forces expected an easy victory and to impose their will on Iraq; however, the post-invasion period was a decade of continued conflict.
( Matazone has new icons, but is keeping this one, Mon 8 Oct 2012, 17:32, closed)

Or, better still
"In actual fact "
(localboy purveyor of pisspoor puns, Mon 8 Oct 2012, 17:37, closed)

I agree with you that before using such an expression
or "in point of fact"
or the politician's favourite "the reality is"

you should be on fairly firm ground that it is a fact. But I don't see any great linguistic advantage "however" has over "in fact".

My personal favourite to use is "as it turns out". It seems you have already researched some mysterious external authority when you use it.
"As it turns out, china has more overweight people than the US"
( cumquat may will not be commenting further on the allegations, Mon 8 Oct 2012, 20:26, closed)