ADSL decreasing speed problem

Can anyone offer any ideas about this problem

When I signed up for ADSL Max I was getting consistently a 1.5 MB download, after a few months it started to fluctuate between 1MB and 1.5MB, then it worked its way down to 1MB and is now down to .5MB.

Line test originally said up to 1.5 MB max, it now says 1MB max.

There have been no changes to the internal telephones in the house, there is no Sky or similar connected to the line. I get no difference whether connected to the main socket, the test socket or extension socket.

ADSL sync speed varies during the day, consistently around 1.5 MB during the day dropping to around 800Kb in the evening/night.

I have reported it to my ISP who have referred it to BT who claim my line is OK.

One further point is that the houses around me all show up on line test as being able to support about a 3.5MB service.

Any comments, ideas, suggestions would be appreciated as I don't really want to go back to a 1MB fixed service.

What is your downstream line attenuation?
It looks like you have a very long line, with plenty of noise on it.
How far away, from the exchange, are you?
If you're seeing no improvement by plugging into the 'test' socket inside the BT master, then you're getting what you're gonna get (unless there's an extension, that you don't know about, wired before the master socket).

I'm amazed you had a working 1Mbps connection. If you're only able to sync at 800kbps overnight, a 1Mbps fixed connection would have dropped out.
If your line attenuation is over 60db (or 62, depending what BT document you read), you'll not be able to have a fixed 1Mbps anyway (although some ISPs refuse to provide a fixed 1Mbps with lower line attenuations).

OK its 6 pm and these are the readings

Sync rate 1216 Kbps
Attentuation 51.9
Noise margin fluctuating between 11 and 12

I'm 3.5km from exchange in a straight line.

Before migrating to ADSL Max I had a consistent steady 1MB connection. On migrating I was syncing consistently around 2200kbps and could download at 1.5Mbps, it stayed like this for about three months, then the sync rate and consequently actual throughput began to decline.

I'm also at a loss to undrstand why my neighbouirs can sync at over 3000Kbps, and the BT line checker confirms their lines can support upto 3500kbps, but mine it reports only 1000kbps (though originally it said 1500kbps, but still significantly less than my neighbours)

I'll post more figures later when the line drops and reconnects.

What router are you using? Perhaps this is failing rather than anything on the line?

Not using a router I have an adsl modem

Its now 2008 line has dropped and reconnceted

Figures are:

Sync 896
Noise margin fluctuating between 11.7 and 12.7
Attentuation 50.8

I note your line attenuation is changing.
This would not normally happen over such a short time period (If your modem is reporting this correctly).
Your stats are truely awful.
A sync of 896kbps then 1216kbps, with a noise margin of 11db, on a line with an attenuation of around 51db is bad.
If you have really eliminated everything, have connected to the test socket [bold]inside[/bold] your BT master, and have no other extensions or telephone cables connected (even ones you may not know about - you don't have an alarm system connected before the master??), then it looks like a line problem.
If you're neighbours sync at 3000kbps (still a little low for lines around 50db), then there's no reason you shouldn't be somewhere close.

Maybe you can borrow an ADSL modem/router to test the line out properly (just in case it's your modem)?