To be in work means to be attending the workplace to me. I frequently work at home, and will say that i'm 'in work' tomorrow, to indicate i'll turn up at the office, rather than work at home that day. Yorkshire native speaker ;)
Is this a Britishism? To me, in the US, "at work" means being physically present; "in work," which is rarely heard, means to me that she has a job, not that she'll actually be at it tomorrow. Which do you folks mean here?
Separated by a common language :-)
You're right, this is a UK expression and it does mean being present in the workplace.
'At work' is accepted for this translation as well and is also used in the UK.
To actually have a job we use possession in English and Welsh.