New Diesel, are they any good and last 10 years?
No chance of any new diesel vehicle lasting 10 years. All the pollution reduction crap stuck in them now makes them complex and unreliable.
Any recent diesel is a bust unless you are driving long distances regularly, which means mostly motorway driving - and if doing high mileage they still won't last anywhere near 10 years because the engine will have worn out long before you get there,
Use one in the town for short journeys and start/stop in traffic and it will be wrecked in just a few years.
How long has Diesel vans got before they are not allowed on the roads
In some areas for vehicles of certain age/type that is already here. Inevitable that it will be spreading to other places.
New Electric: Have they mastered these now they seem to be dropping in value all the time.
They work, however it's a mixed bag - a lot of them are the diesel versions with electric drivetrain shoved in so will be far from optimal - however whether that matters depends on what you will be using it for.
Some used electric vehicles can be had reasonably cheaply. Others not.
Any new vehicle will be expensive and incur massive depreciation in the first couple of years regardless of fuel type - which is why most new vehicles are leased rather than purchased outright. However leasing is of no use if you intend to keep a vehicle for many years.
There are now a few vans built specifically as electric vehicles such as the Kia PV5, but those won't be available used for some time, and new will be very expensive.
Second hand Electric or Diesel. I need something that will last.
Diesel probably a bust, unless you drive large distances regularly and want the immense costs of servicing and repairs that go with diesel vehicles.
Electric could be a solution but depends how far you are driving.
Petrol vans exist.
Just don't buy any kind of hybrid effort as those combine all the worst features of everything with none of the benefits.