Thank you so much everyone. Your advice is much appreciated as this is our first ever campervan.
Second hand ones spec is:
204 engine, 7 speed DSG, ACC, heated front seat, removeable tow bar, awning, shower connection, interior light concept, headlamp washer system, front and rear parking sensors with rear camera, mudflaps, heated front windscreen, wardrobe safe, alcantara seat covers, floor mat. 2018 24k mileage, 3 years warranty left.
New one:
Either 150 (but with no shower hose) or 199 engine (with hose) - I think we prefer the greater fuel economy of the 150?
(but would like to have the shower as we have two sprocker spaniels).
Specifications are cruise control instead of ACC, no electric seat heaters, no heated front windscreen, no mud flats, safe, seat covers, or tow bars. The 150 has LED lights (are these worth having?).
Arguments for the second hand one: It is £2.5k cheaper, 24k mileage on a VW doesn't sound much as they should be pretty bomb proof, it has been very well looked after, you have to pay fewer years of the luxury tax that the new ones come with. Its got a great specification (except its missing the LED lights and the fact it has the larger engine).
Arguments for the new one. Everyone responding to this forum is suggesting the new one is a better option. You get the 5 year warranty and I understand the bellows have a fully opening window.