In reality after 3 years how much money have you spent including upfront payments and deductions at the end due to minor damage? Let's face it you are likely to have a few stone chips on the bumper at least.
I like the idea of it but when I ad the numbers up it puts me off up front £1,600 then £280 a month 3 years limited mileage.
I make it £11680 tax deductible I understand but then you hand the van back left with nothing and start again 
My take on this having been in the commercial vehicle trade;
Both the motor manufacturers and finance houses love that people have become more accepting of renting or leasing a new vehicle. Once a buyer is on the leasing treadmill is more difficult to get off than to continue with a new contract and new vehicle.
A customer is less likely to finish a contract and replace their van with a used one because the future commitment is similar for both - I would rather drive the latest model than an old 5 year old van that someone else has had on lease for the same deposit and monthly repayment.
TBH a new vehicle will always depreciate not matter how its financed.
Leasing is basically financing depreciation with an interest and handling charge levied by the finance house. They also want to sell the van at the end of the contract for a profit.
One thing that's important to consider is the implications about what happens if you have to give up the contract half way through for whatever reason.
There is nothing stopping you selling a vehicle under HP finance as long as its finance 'lean' has been cleared before the vehicle is transferred to the new owner. This is usually more in your control than leasing. With leasing there will be all sorts of financial implications and financial penalties imposed that aren't in your control. This is something which is never spoken about.
Lets take Stephen Burton's van as an example. I don't know how much a top spec Custom is but lets say £20,000.
Stephen has owned his van for 6 months and now finds himself unable to work for whatever reason. To date he has paid £1600 deposit and £1680 in rental payments.
His van has 4000 miles on it and would possibly be worth £12k as a dealer buyback. (That dealer will try to put £1500 - £2000 profit onto the van when selling it to a new owner. ) Already the finance house has a shortfall of £4750 which they have to account for from the leasor. (Dealers love these situations as they become vultures and take advantage of someone else's misfortune when buying vehicles such as this.)
I used to deal with a couple of these leasing houses who had their own internal used vehicle sales departments which had their own financial targets to meet as any used vehicle dealership would have. Anyone could buy used vehicles from them and they would use their own finance house to provide finance. They made a fortune out of some vehicles.