BMW hinted at changes to its sporting M brand earlier this year to Autoblog UK and now we might have some evidence.

Well, it could be, as a document claiming to be a supplier label for brake pads has leaked on to the internet. It lists a model called an M550dX in saloon and estate forms amongst other BMW models.

The 50d could be refering to a new 3.0-litre, tri-turbo, straight-six diesel that is rumoured to have 395bhp and should find its way into both the 7-Series and X6. This engine is expected to be released at next months Frankfurt Motor Show.

Also, historically BMW X models are fitted with four-wheel drive, which is intriguing.

So could this be the first diesel M model? I don't think so, but this could be a high performance, range-topping, diesel version of the 5-Series.