CC: @jriddell

Can you try to get newer debhelper? it is required by quite a few things alreaddy including all of qt

I get more skeptical as I look into this. Debhelper 10 needs
dh-autoreconf (>= 12~)
dh-strip-nondeterminism (>= 0.028~)
dpkg-dev (>= 1.18.23ubuntu3)
all of which seem quite scary

huh? debhelper10 and its deps are in backports are they not?

In T4901#119891, @sitter wrote:

huh? debhelper10 and its deps are in backports are they not?

It is: https://launchpad.net/ubuntu/+source/debhelper/10.2.2ubuntu1~ubuntu16.04.1

The Qt packaging wants 10.3 which is not in backports

In T4901#119894, @jriddell wrote:

The Qt packaging wants 10.3 which is not in backports

Oh. Booooo.

Well yeah, but

a) you could just backport 10.3 on top of that, in backports proper
because
b) dh10.3 is unlikely to need newer deps than dh10.2 I should think (unlike .4 which I see actually moved some functionality into dpkg)
however
c) at the off-chance that it does, looking at the changes in .3 I am not convinced Qt *actually* needs 10.3 but may get away with 10.2 and Dmitry simply put it at 10.3 because it was the latest he tested with (worth asking at the very least)