Demented - I don't think it's that because I do lose the weight, it's just that every so often I hit some sort of trigger which means I suddenly gain lots in a very short space of time. It's just a case now of working out what the triggers are and then avoiding them.
Wheat was the big one, and is still one I'm sure I hit inadvertently sometimes as it's not always obvious, but I'm pretty sure that I've not had any wheat in the last couple of days. I wouldn't be at all surprised to discover that it is the wine, as usually I only have it at weekends, when I'm not even trying to lose, and it having it midweek does seem to correlate suspiciously well with the upwards blips. Could also be dairy though - as I did have a little bit of cheese when I was making dh's sandwiches the other evening.