It is usually possible to park in the front car park of Millbrook Combined School / High Wycombe Music Centre, just off Mill End Road (See detailed map). Please note though that even if the rear playground parking area is open, it may not remain open for the duration of the MEV session and therefore should not be used.
If there is no space available in the front car park, there are several local roads that you can park on. The two main ones are shown on the map below.