The CAA requirement to surrender the PPL is probably driven by the Part-FCL restriction which does not allow a pilot to hold 2 licences for the same aircraft category.
But if the PPL still includes a valid Class Rating, why not just submit a PMD and use the licence within the restrictions of ORS4 No.1283? The 'previous' part simply means that the licence holder must have made a PMD before operating within the terms of the restrictions.