We once spend months looking for Mrs Snoopy's old "Nursery Carpet" ~ cotton, large and v expensive to buy nowadays. Then we remembered that the Fire Brigade had used it to stop up a hole in the roof of our last house, when a storm brought half the chimney down through the tiles. The Brigade (just to give the details for those who I know will demand them) had been summoned as there was a danger of further damage (a gale was blowing and it was 2 o'clock in the morning ~ you try finding a builder). The Fire Officers bunged up the hole with a "Bit of old carpet we found in the loft" and then sheeted the roof with tarpaulins ~ leaving us to get it sorted the next day. Heroes all I felt at the time. BUT the point is we forgot about the carpet until we came to look for it after we moved two years later. It then took months before the penny dropped.
I should search any out buildings, attics, lofts and garages as well Nick. It'll be there somewhere and then someone will clap a hand to their forehead and say "Of Course ~ don't you remember when ..... "

Go back over every leak, draught, cover needed in a hurry for whatever reason, that has happened since you last saw it. That's what we ended up doing
Anyway we already know whose going to be to blame don't we?
