The Ultra Low Emissions Zone now covers everything within the M25. It'll be worth opting for a petrol vehicle, as most cars registered after 2005 escape the charge. For diesels, it's only cars registered after September 2015, limiting their choice to much newer and thus more expensive vehicles.

The successor to the Xsara Picasso is the C4 Picasso, although it's a little bigger. There's also the C3 Picasso. A used Skoda Yeti could also be worth a look, although it's more of an SUV in style, rather than an MPV. Depending on the budget, they could also consider the Seat Arona, which is a compact SUV that's similar in size to the Xsara Picasso (if a little smaller).