It looks like this service is intended to replace the kind of random "notify us of a missing manhole cover" type forms that are found in their thousands on government websites. For those types of applications, emailing the form to a relevant mailbox is probably the correct thing to do, and in many cases it's the way the existing forms already work. Only a small fraction of government services will have their own custom backend application supporting them.

The main intent here is for non-technical folks to be able to replace the tens of thousands of PDF forms, not for technical ones to use it while building actual services.

I get the sentiment, but an email is just a standardised queue. What were you going to do after the HTTP PUT? My guess is it onto a queue.

It's a standardized queue with a lot of features too...

You can set up filters and forwarding rules. It doesn't require a programmer or special knowledge to do so.

The queue can be viewed by one or many humans.

Messages don't have to be dealt with in-order.

read/unread state, stars, labels, drafts all allow construction of advanced workflows with no specialist knowledge.

Sure, all these things can be done better with special software, but there is a massive benefit to something that all your existing untrained and probably-not-well-paid employees can set up themselves.

Old school HTML Forms don't require an active backend. They can be a purely static site.

> surely HTTP PUT of an XML or JSON document to a user nominated URL

This is the bit that's more tricky than a static site. And then you need to do something with the data.

You can optionally pass an onSubmit function that will return the fax number that the form should be submitted to after printing.

it is really cool but at the same time I can not stop smiling when the governement is telling you of about the best practices how to use web technologies, it is just funny

As far as I know, the audience for gov.uk forms is teams that have no developers. So for that audience, email is very much the right approach.

Often the thing you are replacing is 'fill in this pdf and email to this inbox', so it allows people to improve things for external users without changing their workflow.