We sent off for my wifes citizenship and as requested, included my passport. However after a couple of weeks I needed it back as I was going to Latvia. Eventually I got through to the right person and arranged to get it sent back for the sum of £5. They said that they might need my passport back, but why? My wife already has ILR, has a valid Schengen visa in her passport and has sent in our marriage certificate- all of which she couldn't have got without proof of my British citizenship. Seems totally unnecessary to me.