gradually reducing speed after several IP changes

[#1]

Had 3 IP changes since mid-July.
Each time the IP alters the speed gets less.
Nothing at all has changed here, same set up as ever. (Including my usual internet acitivity.)
I was getting terriific speeds back around June sometime.
Just wondering why the IP changes have become so frequent (used to have the same one for a month or longer).
Will it improve again, or is this a permanent downward spiral?
EDIT - twice lost connection here while trying to post this!
          but still appear to have same IP at least.

[#2]

Hi there,
The IP changes will be down to drops in connection, but we're not seeing them anywhere near as often as you are:
<img src="http://community.plus.net/visualradius/generated/image13758725271687.png"/>

Are you using a wireless connection by any chance, and if so do you get the same errors when your PC is connected to the router with a network cable?

[#3]

Thanks for your reply, Matt.
These are the IP changes I have, getting more frequent.
With each IP change over this period my speed is gradually getting slower and slower.
146.90.217.58 -   24 jun
87.115.41.212 -   29 jun
91.125.147.59 -    2 jul
46.208.170.85 -   11 jul
146.90.152.246 -  6 aug
146.90.29.38 -      6 aug
84.93.52.96 -        7 aug
46.208.97.202 -    8 aug
84.93.100.* -    9 aug
Wired connection only, btw, don't use wireless.
I don't expect the IP to stay the same all the time, of course, but its a bit worrying that the speed is on a downward trajectory, and getting to the point where it changes every day.

[#4]

Well, the profile isn't changing (it's around 17Mb at the moment) so I suspect the best thing to do would be to run a BT speed test or two (http://speedtest.btwholesale.com) when the line isn't behaving - that'll give us an idea of the performance and also some ammo if/when it becomes time to raise a fault.