Sheds. Not places for a bike. Something similar happened to me. Possibly opportunist though, sheds are easy targets and People will unscrew your shed door just to take a look inside and bingo, there is a shiny new bike for them to take. I don't think the police take shed crime too seriously so the risk/reward ratio of burgling sheds is in the thiefs favour IMO.
Do not keep your replacement bike in the shed again. They will wait for your insurance to come through and take another look inside in 6 months or so.
Read my OP again - I know what you're getting at but it wasn't a complete bike, it was in build, literally just a rolling chassis with no drivetrain, seat or even tyres. It weighed the think end of 25lbs so it wouldn't have been easy to carry. It was all parts that I'd bought off eBay for little or no money. There was other stuff in the shed which was more valuable and more "fence-able" such as hand tools and power tools.
No other sheds or garages have been broken into and aside from my neighbour (who actually lives on the other side of the village, so it could be unrelated) who's car was broken into, no other properties have been targetted. It's impossible to see the shed from the road without venturing well onto the property.
No, somebody knew what they were after and where it was.
There's a little bit of good news - the rozzers came within an hour of me reporting it and sent a CSI unit to photograph a very clear footprint which I found. The forensic guy knew immediately what make and type of shoe it was without even looking it up and even though he didn't say it in as many words, he more or less intimated that he had a good idea who it might be...