Well you can be sure we don't run our network at any where close to this, we are scaled to allow people people with Gigabit connections test their speed.

It could be many, things a broadband connection itself is usually slow or fast not very variable, so suggestion is that it is NOT the ADSL itself, but a PC/router/Provider network/wholesale network issue.

Thanks, that's pretty much what I thought would be the case.

I've carried out the speed tests using two different PCs and a laptop, plus three different routers. All combinations show similar characteristics, so I'm pretty sure it's not my equipment.

To be fair, I've been with PlusNet for many years and they've provided me with a broadband service through 5 or 6 different exchanges, and I've never seen this problem before, so I'm not sure their equipment is the problem either, especially as I am currently on a Market 1 exchange.

That leaves BT.

I'll chase up PlusNet and see what they say.

Interestingly, since my sync speed has halved (the other post you've replied to) the shape of the speed test graph looks better.

What is your view on the likely reason for this?