I am looking at replacing my fencing with some elite type panels.

I will be changing the posts too.

If the panels are 1800mm, and I use a 150mm base gravel board, would a 2400mm post be suitable (450mm or 8 inches in the ground)?

Should I go for longer 2700mm posts?

Second that.

Have you checked B&Q?

I'm a bit pissed off because my local branch no longer stocks treated KDS, it's all planed to match in with the rest of the decking stuff (presumably for H&S reasons - no splinters), including posts, although not sure if they do the longer lengths in PAR.

Yes that will be fine.

You can put up a 2m fence without planning permission. That used to be 6ft but we've gone metric. Many fence panels are still nominally 6ft which is 1800mm.  Basically your 1800mm fence panel probably isn't intended for use with a gravel board but if you can get posts tall enough posts that's no problem as 1800+150 is still under 2m.

With a curved top perhaps best to work on the peak height or the average at least. The latter would be..

1700+150 = 1850
30% of 1850 = 600 approx in the ground.

Posts need to be..

600+150+1600+50ish = 2.4m

If you can get taller posts you need not dig the holes exactly the right depth - you can just dig them roughly 2ft and cut the tops afterwards.

Thanks.

Planning not so much an issue - It is a replacement fence anyway.

Oddly, where we live on a small estate built in 1978, there is a covenant on the deeds of all houses saying the fences will not be more than 3ft at the rear, and 1ft at the front!

There is not a single house than complies to this at all any longer.  All houses have 6ft rear fences and 3 ft walls out the front with hedges in behind.

There is also a covenant that you cannot keep a caravan on your drive or in your garden........That you cannot have bonfires.......

Yea, postcrete is the stuff to use - One bag for each hole, or perhaps one and half?