Are there any photo's of the job in hand? I've seen the BMC filter at £67 on fleabay
http://www.ebay.co.uk/itm/271652081053
No photographs unfortunately because I thought it was going to be a straight forward job. In the main it was. However, whoever designed the airfilter box was either drunk or had a malicious streak.
When I removed the wheel and inner wheel arch (straight forward) the plastic cube holding the air filter had 4 small bolts on the observable side
these were easily removed either by socket or philips screwdriver.
Be aware that the front doesn't just detach but the front, bottom and outer sides detach in one piece.
Also the shape of the BMC filter is a slightly different shape from the oem version in that the oem version has completely round ends. Although in practice this makes no difference to fitting it into the airbox.
That does seem a good price. I bought mine from for £74.
Mike