This design is recorded by the version in the National Gallery of Art, cited here. As there are only relatively few surviving impressions of the design (see Nancy Bialler and Freyda Spira 'An unpublished proof of the Arch of Honour of Maximilian I' in 'Print Quarterly', March 2021, pp. 3-16), the possible link between Charles I's impression sold to Col Webb and the British Museum impression (inv. no. E,5.1) bequeathed by Joseph Nollekens in 1834, remains to be investigated. See: https://www.britishmuseum.org/collection/search?museum_number=E,5.1). Thanks to Giulia Bartrum for this information.