Will this fit a mountain buggy urban double?

Hi Natalie, thank you for your enquiry, the Britax stroller organiser is suitable for use with most strollers as it has adjustable straps, however, due to the Mountain buggy being a double I can not confirm this. We hope this helps. If you follow the link https://www.babyonthemove.co.nz/store-locations/ this will take you to our online store finder. Here you can find contact details for your nearest Baby On The Move Store where one of our team experts will be happy to assist you in your product search and help answer any further questions you may have.