Help!

[#1]

You don't need the filter when connecting to the test socket, so ideally you just use the plain adaptor supplied with most routers. Having said that, the figures from the Netgear router are a lot more believable than the original one. I would suggest there may be a number of problems here.
The original router is not reporting the stats properly, and may have other problems, so is probably best replaced.
The noise margin is quite high, which suggests a noisy line, possibly made worse by questionable extension wiring.
I think the best thing to do is get a new router, put the faceplate back on the master socket, and, if possible, leave the new router plugged into the master socket for a few days and see what happens. If the sync rate stays where it is you should get a profile of 4500, maybe 5000 kbps once the exchange catches up.

[#2]

Just an update, about 2 weeks ago the speed on my broadband suddenly jumped up and I was getting about 4000kbps which I was happy with... i had started using the netgear router instead and so I presumed it was because of this, although the speed imrproved a few days after i started using it...
Anyway speed has randomly dropped again to about 1500kbps  I have changed nothing whatsoever, am not over my limit or anything like that...
I dont get it?

[#3]

Bt speedtest results:   
Your DSL connection rate: 6336 kbps(DOWN-STREAM),  448 kbps(UP-STREAM)
    IP profile for your line is - 4500 kbps
    Actual IP throughput achieved during the test was - 1877 kbps

[#4]

That looks like the BT Performance Tester giving suspect throughput figures as it often does of late. What speed do you get using the thinkbroadband tester?

[#5]

I dunno, the thinkbroadband one doesn't work for me. Have the port opened and everything too.
speedtest.net gives around 1900 kbps

[#6]

Do you have a Java Runtime Environment installed? Read further down the TBB page and it will tell you where to get one.

[#7]

Quote from: Bobby505

.............................................Anyway speed has randomly dropped again to about 1500kbps  I have changed nothing whatsoever, am not over my limit or anything like that... I dont get it?

Well, you've got an intermittent problem somewhere! Forget the throughput speeds for a while, we need to concentrate on getting a stable sync speed, you've obviously had a low sync event recently for your profile to be down. What speed profile have you got at the member centre https://portal.plus.net/my.html?action=data_transfer_speed (login required)?
Need a bit of a recap. I've re-read the thread, and there's a few things remaining un-asked/answered.
A few tips before we get started - don't just unplug the router from the line at any time, power it down first and wait about a minute.
Don't do this more than about 5 times in an hour, otherwise the exchange DLM may think you have a problem and possibly raise your target SNRM resulting in lower sync speeds. If you get to this limit, I would not do anymore for the rest of the day. Re-syncing after dark will generally give lower sync speeds as noise levels are worse.
Did you ever discover why you couldn't get sync when plugging into the test socket and is it OK now?
The boiler cupboard is not a particularly nice environment, probably too warm, contacts can oxidise. Powerdown & disconnect the router as advised.
Remove the master face plate and take a corded phone and plug it in & out of the test socket several times to try and ensure the contacts are clean. Now pick up the phone, you should have dial tone, if not wiggle the plug around to see if that makes a difference, with your knuckle tap the rearplate above the test socket, is there any crackling or other intermittent noises? If you have dial tone and there are noises phone your telephone service provider (151 if BT), do NOT use any automated tests, speak to an adviser, get them to confirm they can hear the noise and log it as intermittent. State you are plugged into the test socket, ask that all that information is passed to the OpenReach Engineer. Do NOT mention the broadband - you are reporting a voice fault.
If all OK so far, check the following, that there are only 2 wires connected to the back of the faceplate a Blue/wh & a White /Blue to terminals 2 & 5 and that they seem secure in the IDC terminals (no orange wires should be connected). Replace the faceplate and repeat the phone plug action in the master socket and check the line again.
More to follow.

[#8]

The two "slave" sockets that weren't proper slaves. Check that the wires seem secure in the IDC terminals. Which do you normally plug into, the one with 2 lots of wires, or the other one?
Check that there are no orange wires connected to either. Did you snip off the 3 components off each socket, that's the capacitor, resistor and surge arrester. If not, do so. Repeat the plugging in of the corded phone in both sockets and check for noise.
OK, that's the wiring checks out of the way.
Have you noticed if you lose sync at any particular time of day on a regular basis. I'm assuming you leave your router on 24/7. If not, you should consider doing so. If you switch on near or after dusk, line noise is likely to be higher and sync speed will be lower. I'm assuming that you are still using the Netgear router. You should consider downloading and running RouterStats. Your computer will need to be on for monitoring.
Finally have you tried another filter? The one you are using looks like a good quality one similar to the BT MF50, but they can go faulty.
I'll leave it there for the moment to wait for you to respond and see how you are getting on.