There appears to be no general enquiry number, so sent an email via the contact form, which should at least go to the parking department. If there's no joy, I got in touch with the bods who run the official Wembley Arena/Stadium parking, the option of bike parking wasn't showing. However, a nice lady enabled it again, so I could buy a space in their multistory for a fiver (did that for Underworld a couple of years back).