I've drawn the layout and calculated number of boards assuming that because they are tongue & groove (and boneded with foaming glue) it does not matter where they meet.

However reading now advanced fitting guide it states: All short end joints should always fall on the centre of a secured joist including perimeter edges.

 

Is that the case in practice?

 

Of course in my refurb joist spacing appears to be random, if I was to follow that rule, instead of 3 boards per row (7m internal width, 3x2.4m boards should do it) I probably need another one for each row, if the previous 3 are chopped to match the joists. And is square edge sitting on the joist more rigid than suspended glued tongue & groove?

In practice, the boards are generally just laid wherever they fall. We’ve never had issues with movement on an unsupported end as long as glued well. Any squeaks/noises are generally down to not enough glue/nail missing joists. 
Having said that, most of the joists we work on are 400cc. 

I have never done that with short ends, with proper glue it becomes one piece, never had a problem and no squeaks!

Glue it and it should be fine, if you are worried about the joint put a couple of noggins in to support the joint

Sounds like a plan: on landing (only 2 boards side by side) I'll add noggins under the joints.

In the rooms I will just go with the flow: with many neighbouring boards, each shifted by half width, they will hold the short ends from either side. 

Recently I replaced the whole ground floor of a bungalow (woodworm) and only supported with noggins short ends where a square cut was needed (doorways etc).

Building regs are joined on a joist or supported by a noggin  

Though I could not find that in builing regs, there is actually a nice chapter in NHBC standards.

It also mentions 'long edges at room perimeters should be fully supported on joists or noggings' - oh well, I've got 2 more rooms to improve

Though in my defence the existing floor (T&G planks) did not have that feature.