Fingers like lightning
They are doing their job, i.e. vetting candidates to make sure they are allowed to work here...
They're legally required to verify your right to work in the UK, and they do that using your passport. They want to meet you to make sure that you're the right person for their client. I've worked for Michael Page before and this is their standard procedure for a new candidate. If you think about it, it makes sense - they want to portray themselves in the best possible light to their client, and therefore put forward only the best candidates. Verifying the candidate for themselves before sending him to a ClientCo interview allows them to be certain that they're not putting forward a drooling primate.
Personally I find it's a vastly more professional approach than that taken by most of the dodgy operators out there, and it's one of the reasons why I still have the occasional beer with my Michael Page recruiter even though I haven't contracted through them for almost two years.
Hmmm, I wonder if I put a request to a agent that all candidates must have a banana in their top-pocket (ala Milliband) and have their left trouser leg rolled up to comply with our grand lodge requirements whether they would send me any candidates.
Nothing to fret about, bit like internet dating.
Never has a man been heard to say on his death bed that he wishes he'd spent more time in the office.