Kamikilla ....
I echo what xebec & Joe Bloggs say.
In our case (and I guess in many other's) we merely stated on the application form "as soon as practically possible"
in regard to the marriage question.
We did not enter any further details, or produce/show provisional bookings etc.
So, the question is.... has this "request" come from the ECO at the British Embassy, or the legal people you've employed ?
My first thought is to ask to see the actual request for further info.
If it's correct .... it's a really strange request, as it's physically impossible to do much more than provisionally book anything.
... and to be honest, that really ain't worth the paper it's written on.
As Joe Bloggs mentions .... I think it's really to do with your (past/historical) relationship.
You've gotta convince them that you are genuine, you are a partnership etc etc.
You've gotta show visits (passport stamps), hotel bookings etc etc .. photos over the whole period.
Perhaps I'm second-guessing the ECO here, but in your profile u say u are 22yrs old.
So, if you've been an "item" for 6yrs ...... then you were 16yrs old when u met ????
Perhaps that's what has caught their attention ?
