I found the answer in dconf - I changed org.gnome.desktop.input-sources sources from:

[('xkb', 'gb')]

to

[('gb', 'xkb')]

This works very nicely, but seems to have killed the Keyboard Settings:

Probably as I switched iBus and the other thing in a 'incorrect manner' - here is the description of the thing I edited from dconf-editor:

Schema:

org.gnome.desktop.input-sources

Summary:

List of input sources

Description:

List of input source identifiers available. Each source is specified
as a tuple of 2 strings. The first string is the type and can be one
of 'xkb' or 'ibus'. For 'xkb' sources the second string is
'xkb_layout+xkb_variant' or just 'xkb_layout' if a XKB variant isn't
needed. For 'ibus' sources the second string is the IBus engine name.
An empty list means that the X server's current XKB layout and variant
won't be touched and IBus won't be used.

But as it works still, I'll leave it until it explodes or something.

Update:

Setting it to this also works:

[('ibus', 'gb')]

Weird.