Max. Bandwidth Down/Up(kbps) 3252 / 1056
Bandwidth Down/Up(kbps) 258 / 251
SNR Margin Down/Up(dB) 27.0 / 30.2
Attenuation Down/Up(dB) 48.0 / 29.2
And your problem is there.... Basically, ADSL works by sending a signal of known size to your house. The box sees how much signal is lost (the further away you are, the more signal is lost) and calculates the loss in deciBels (or dB). From the reading there, it sees that you lose 48dB because of your distance from the exchange. What the system also does is give you a margin to allow the signal to fluctuate - my margins are 6dB, yours is 27 dB which is HUGE. Consequently, the system is only syncing you at 258kbits/s down where if the margin were lower, you would get much higher. This isn't about a poor congested ISP provider, but your line to the exchange not syncing at a high enough speed.
The first thing you will have to do is take all phones out of all sockets, isolate any extensions and plug your modem/filter into the BT master socket (if the computer is wireless, only the router needs to be moved - you won't be doing a speed test). If you have one of the newer BT master sockets (see this link
http://www.thinkbroadband.com/tools/bt-master-socket.html for identification) where the bottom half is user removable as shown in the expanded diagram in Step 3 on the page I linked to, you are best removing that and inserting your modem/filter into the uncovered socket. Redo the test s above and see what the bandwidth down/up is and what the SNR margin is (the first should be somewhere between 6 and 12). If it is as you've shown above there are two possibilities:
1) A problem with the configuration of the line - something has set the equipment in the exchange to give you a massive buffer for changing signals. This might be a mistake or it might be because of 2)
2) A problem with the line back to BT that causes its quality to fluctuate wildly during the day causing something at the exchange to set a massive buffer for changing signals
Basically, if you plug your router into the Master Socket and those figures stay the same, there is a problem that BT/your ISP have to fix. Start with your ISP and ask them why your profile has such a high signal to noise ratio on it. They should be able to look (or get someone to look) at what the equipment in the exchange is doing.
There is also the possibility you are still on one of the old ADSL profiles. My attenuation runs at 54dB (yours is 47) and I get 4Mbit/sec. With a 48dB loss, I'd expect you to get between 4 and 5 Mbits/sec down, but if your modem is configured for the wrong type, you will get slightly lower speeds.
Apologies if this is all gobbledy gook... but you're going to have to isolate the problem (internal wiring vs from the master socket) and tell your ISP/BT to sort out the fault (assuming it's outside the house).