Car covers with "windows"

[jonk]

Anyone know of any decent car covers that have transparent windows in so that you can leave the tax disc / parking permit on display?

I sometimes street-park in London, and would like to cover the car, but don't want some over-enthusiastic traffic warden ticketing me because he can't be bothered to lift the cover.

Any thoughts (other than an Argos cover, one of those see-through document wallets and some gaffer tape?!)