I have a 54 reg 2.0L TDCI Mondeo 130bhp. I bought it about a year ago and it has done about 96k miles.
Since I've had it, I've averaged about 56-57mpg. However, in recent weeks, this has dropped down to 53-54 mpg. I'm not aware of doing anything differently so can't work out why it's dropped so much.
Sometimes it does drop, but then it increases when I do my usual 28mile trip into work each day. This hasn't been happening of late - it's only been decreasing.