Purchased, thanks for the heads up, normally get the filter separately so this works out much better value.
It's a constituent part of the Cat & Dog pack. When you buy any of their Cat & Dog vacuums across their ranges, it's this type of filter (and a turbo brush) that is a standard fit item in order to be able to call it a Cat & Dog version.
Hmm, OK. I have clicked through the promotion and I just don't see the (free) addition of the SF-AA50 filter (at the checkout):
for the packs without the Active filter it's £18.99 (comes with the standard filter membrane that you swap out within the post motor filter cage). For £22.99 you get the pack that also includes an Miele SF-AA50 active filter which varies in price when you buy separately anywhere between the £8 to £23 mark. Currently just the filter is £15.86 on Amazon.