In reply to James Malloch:
As Hooo says I think charger/jump starter are normally separate products.
I have a Noco GBX45 jump starter (https://toolstoredirect.co.uk/products/noco-gbx45), which has been great. Claims to do diesels up to 4L which I imagine is more than enough for most people.
When I've used it I've found it's not quite as smooth a start as normal, I seem to need to hold the key in the ignition position for a couple of seconds.
Successfully started my 2.0 Peugeot Boxer (diesel) when it was totally flat (had been flat for weeks) and it was <0°C. Still showed 3/4 charge afterwards.
It's pretty compact, would easily fit in a car glove box. As an aside - Lithium ion batteries are so great, the equivalent product in the past would have been huge.
My only complaint is the the leads coming off it are a bit short and don't quite span the distance between the jump start points under the bonnet in a boxer. The leads are long enough to span between the terminals of any car/van battery I've seen though, so it's fine.
It has a useful feature that there's an override button which turns off the safety checks, so you can use it on totally dead batteries (just be careful if you use the override that you've definitely got it hooked up correctly!). Don't know if other brands have similar, but worth checking if you'll need to use it on totally dead batteries.
The brand has various sizes available, I think I might have gone a bit too large for what I need. Downside of going too large is cost/a bit of extra bulk/weight. Upside is I know it'll start the van even in the worst case scenario and it will have charge spare after doing so.
There are cheaper options available (e.g. Halfords own brand, Amazon) but I decided to go with Noco because they seem to have a pretty good reputation and being stuck somewhere with a car/van that won't start can be quite sad.