Hi Guys,
I'm flying LGW-LIM tomorrow 12:20 BA2239. The plane has a 3-3-3 seat combination in economy. I checked in this morning hoping for a window seat, but the majority the left and right aisles (seats ABC, HJK) have been blocked out on the check-in, with almost every middle aisle (seats DEF) still available.

I phoned up BA and they said that these seats are mostly not taken by people but have been blocked and they are only available on request at the airport.

Is this normal? I'm not a frequent flyer so I don't know if this is standard procedure.

If so, would I have any chance of asking for a window seat at check in tomorrow?