Ok that isn't the problem then. Do you need to have the extensions connected up?

Not necessarily, and I am still willing to experiment with disconnecting. But I have ordered this supplementary faceplate, so I will see how that goes first.

Ok can you connect to the test socket and run a speed test using Ethernet.

Ensure the wireless is turned off on your laptop.

Do you get 25Mbps?

Finally what laptop are you using for the test - it is possible the wireless card inside the laptop is not very good.

I always recommend naming the 5ghz and 2.4ghz networks differently, you should do this as well. If you need help doing this look here

http://community.talktalk.co.uk/t5/Community-Help-Ar...

For now just keep the channel on auto, but change the wireless name for 5ghz.

It might be useful to try the Quiet Line Test on that Alarm Master Socket, as it is likely that its outside wiring runs alongside your other (BB) line for some distance.

Update 1) I did the quiet line test on the alarm line, and it was silent, so that seems OK.

Update 2)

OK, so I have received and installed the interstitial faceplate, and it seems to have solved half the problem. Where previously downstream speeds for WAN were 25 Mbps in the test socket and only 7 Mbps in the faceplate, the router is now plugged into the new, normal faceplate socket and WAN speed is at 21-23 Mbps, which seems fine to me (close enough anyway, particularly accounting for some variability).

However, the other half of the problem still exists. I have done everything you have all suggested and speeds to devices have not improved. I brought down a desktop and connected it to the router by ethernet, I re-ran speed tests on my S5 phone and my laptop, I renamed the wireless 5G strand (and I did tests separately, so tested the ethernet with all wireless devices disconnected), and speeds are still the same. All between 6.5-6.8 Mbps.

So at this point, I'm thinking the router must be the issue. If the router is getting speeds of 21-25 Mbps from the exchange (so interference from internal wiring has clearly been eliminated), and even a computer on a wired ethernet connection is only getting 6.8 Mbps, there must be something wrong with the router's output, right?

For the record, my wireless card is the Intel Centrino N 6235, which actually does have some issues (probably driver related) and occasionally crashes bringing down the computer with it. But mostly it works OK, and it certainly should allow sufficiently high speeds. And in any case, three devices are getting exactly the same speeds, including a different computer on a wired connection.

Is it time to contact TalkTalk and demand a new router...?

Oh, and in case it might help, I've pasted most of the router/wireless settings here that seem potentially relevant:

DSL Connection Status

Internet Connection
DSL synchronization status: Up
Connection status: Showtime

Line Quality
Upstream line rate (kbit/s): 2000
Downstream line rate (kbit/s): 21462
Upstream noise safety coefficient (dB): 13.4
Downstream noise safety coefficient (dB): 6.1
Upstream interleave depth: 1
Downstream interleave depth: 2417
Line standard: VDSL2
Upstream line attenuation (dB): 11
Downstream line attenuation (dB): 25
Upstream output power (dBm): 6.9
Downstream output power (dBm): 10.3
Channel type: Interleaved
DSL up-time: 0 days 5 hours 59 minutes 53 seconds

System Information

System Information
Product type: HG633
Hardware version: H.1.01
Software version: v1.15t
System up time: 5 days 1 hour 18 minutes 13 seconds

2.4 GHz Frequency Band
ON/OFF: ON
Security mode: WPA-PSK/WPA2-PSK
Channel: Auto(9)
Transmit power (percentage): 100%
Region: Great Britain

5 GHz Frequency Band
ON/OFF: ON
Security mode: WPA-PSK/WPA2-PSK
Channel: Auto(36)
Transmit power (percentage): 100%
Region: Great Britain

Broadband Information
DSL synchronization status: Up
Connection status: Showtime
Upstream line rate (kbit/s): 2000
Downstream line rate (kbit/s): 21462
Maximum upstream rate (kbit/s): 4780
Maximum downstream rate (kbit/s): 31200
Upstream noise safety coefficient (dB): 13.4
Downstream noise safety coefficient (dB): 6.1
Upstream interleave depth: 1
Downstream interleave depth: 2417
Line standard: VDSL2
Upstream line attenuation (dB): 11
Downstream line attenuation (dB): 25
Upstream output power (dBm): 6.9
Downstream output power (dBm): 10.3
Channel type: Interleaved
DSL up-time: 0 days 6 hours 30 minutes 13 seconds

Beyond that, a few other settings that might be relevant:

- DDNS is not enabled
- All 3 dynamic routing options are 'Passive' and 'Off'
- Operating mode: Auto
Current connection type: VDSL

Then there are some statistics for LAN, Wireless and Internet, with a table in each section with columns for Interface, and Received/Sent Byte, Packet, Error, Discarded. I can paste these if useful.

Thanks everybody.

One last check that I can think of. I hope you still have the desktop machine down there.

It often happens that after connecting wired, while wireless is running on that machine, that it takes a while for the ethernet to take over the connection from the wireless. If it ever does. I've been caught out a few times that way.

When I want to swap, I now make sure I either disable the wireless on the computer or go into the Network page in Control Panel and make sure I disconnect it there and that the ethernet is in charge.

Ha, thanks for the suggestion, but that's definitely not the problem, as the machine doesn't have wireless...

I'm teetering on the edge of calling in, but might wait a bit for any other suggestions first.

Just can't see how it can be anything other than the router now, unless I fundamentally misunderstand this system (which is admittedly perfectly possible...).

If the router is getting the right speeds from the exchange, and 3 separate devices, connected both by wireless and cable are all getting similar and severely restricted speeds, that seems to point to a router problem to me...

Try turning off the broadband hardware for an hour.

Why this might work, is that some providers use a mirror of a 'connection speed' setting and limit traffic based on that. This normally affects PlusNet users, but believe you are with TalkTalk and so this should not be a factor, but it is possible that all the kit at your end is now OK and needs the providers end to notice the connection speed change.

An hour off, gives their systems time to expire your connected session and relearn you when you connect again.