Unless you have the full permissible 30% deposit*, doing a PCP at 4 years isn't going to have you breaking even (what the car is worth vs what you owe on it at that point) until you are approaching 3 years into your 4 year term to allow you to change.
Take a 3 year PCP and you'll be breaking even at around 2 years. Don't forget that on a 3 year PCP, about 1/3 of your monthly payment is interest. It's even more on a 4 year PCP - in any given month you'll be paying off less of the depreciation and more of the interest on a 4 year deal, and the car will obviously be worth less at 4 years old than 3 years old.
On the VW website, to finance a bare bones GTD, there's £37 difference between a 3 year and a 4 year PCP. If you can afford the extra then it'll give you a lot more freedom on a 3 year term.
Also remember, extras will tie you up longer and cost you a lot per month on a PCP deal. The car depreciates about 50% in 3 years to the GFV (you might get 55% of RRP in p/x value), but it's 80% depreciation on the extras. You take a £25k GTD and it might lose £11k over 3 years to what you get in p/x. Start adding £5k extras, and you've lost £15k in the same period. That's almost a third more money on your PCP!
*30% deposit is considered as the difference between VW's RRP for your car and what you are financing. If you get a 12% discount on a £25k car then you only have to find £4000 of that £7500 "deposit" from your own money to max out the deposit and minimise what you owe at any given time.