Lower sync speeds for the last 2 months

for the first month or 2 on max i had a sync speed ussually between 4000 and 5000
my download speed was a steady 480k/sec i believe , the odd time i would get 540k/sec

but all of a sudden it dropped to a 2.5meg speed (300k/sec) and has stayed there ever since
my sync speeds struggle to get above 3000 now
this was around the time i had sky tv installed , but ive tried unplugging the sky phone line for long periods (days) and it doesnt make any difference , same with my other 2 phones
all connected as they were through microfilters

i use a Netgear dg834G v2

any thoughts?
(it was also rather hot weather all the time when this started)

My first thought would ring wires.

I'm assuming here that Sky added an extension for your box when it was installed and that's been run from the master socket.

Unscrew the bottom half of the master socket and look at how many cables are connected for the extension - 3 I'd guess.

It should be the orange wire - the line should be blue/white and white/blue.
If this is the case, cut the orange wire and reboot the router.

i installed the line for sky myself , but its just plugs into a microfilter and can be completly removed at anytime , and has been for the last few weeks

i used to sync at say 4700 ish and my noise margin would always be around 6 , now i sync at 3300 ish and my noise margin is around 15 , seems to suggest theres more in the tank so to speak , but something stoppin it , i lean towards my router being the problem but not sure , guess ill have to try a friends

If you've got a 15dB margin, then that'll be the problem.
The standard DLM target margin is 6dB, so your DLM settings have changed for some reason.

It's possible all the lightning recently caused your line to drop enough for the DLM to start upping your target margin.

Drop support an email at support at aaisp dot net dot uk and ask them to look at the target margin on the line and if it's not 6dB ask them to get BT to change it back.