[arobwk]

Here is a diagram the post I am talking about has a question mark on it.

A few thoughts @Hogwarts
Edit:  just realized fence is already done/complete - my old grey matter hadn't immediately registered the fact (ref' your post earlier today).  However, I'll retain my posted comments and add a question later.

Re the run with slight bend at bottom of triangle:  my Clipex-system beefy metal posts are advertised as taking a 15 degree bend on a strained fence without bracing and I've done that - it works.  Therefore I would say a stout timber post could take pretty much the same (and I know of several stock fences that follow long bends without bracing).   For the 15 degree test:  measure 2m from the post in question each way along the fence line/s towards the corners, then measure between the 2m points - a measure of 3.966m or less (error - oops!) or more will mean angle of 15 degrees or shallower.  A horizontal bracing piece could also be dug into the ground at a shallowish depth to help brace the post against the strain. 
Another way of dealing with shallow bends is to use more than one stout post spaced several metres apart, but it then becomes a toss-up between digging more than one post in and the effort involved in bracing a single post !!

Re fence tension: I've only worked with high tensile line wire (i.e. not stock mesh) and using a tension gauge.  However (at risk of teaching granny), the stock netting will have been manufactured with kinks in the horizontal wires every now and then:  when these kinks are pretty much straightened out by the tensioning, design/recommended tension for that particular netting is reached.  I would think that a little bit less tension would be OK if you are not stocking to high density nor keeping larger breeds to maturity and especially if you add an electric line.

Re spacing and sizing of inters:  I see so many variations on the spacing/sizes of inter posts (on what are clearly viable, long standing fences) I would not wish to make any definite suggestions.  However, as a general thought, if you are doing everything mandraulically, driving more smaller diameter posts will likely be easier/quicker than digging holes for fewer but larger diameter posts !!

Edit:  What did you do about the slight bend in the fence line in the end ?

[Hogwarts]

Edit:  What did you do about the slight bend in the fence line in the end ?
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I put struts/ bracing  in as instructed by SallyintheNorth. I shall be keeping an eye on it going forward however for any potential leaning. There is a ditch and a hedge bank immediately to the right of it so not sure the moist ground will help but I'm thinking some sort of third strut into the bank to stop any lean dead in its tracks should sort it out should I run into difficulties.