i should know this but what does it MEAN to have a mortgage in place?

[oranges]

Every EA asks this, but surely a mortgage is only offered on an actual property - once the surveys are completed etc. I know you can have a rough idea of how much you can borrow, but isn't that it?

Basically what they want to know is, is it too late for them to sell you a mortgage or have you decided who you are going with.
You can get a mortgage agreed in principle and a certificate to prove it, that will become more and more important as lending tightens but for now just smile and say yes, then go to an IFA and get them to arrange the best deal for you.