I’ve noticed a pattern to my problem.

[#1]

I'd honestly save your time and trouble and go for another router from those I have already suggested.

[#2]

Hi MickKi,
I was just about to buy the Speedtouch you mentioned when a friend of a friend offered me a ‘D-Link DSL 2740B’ for £35.  Apparently he bought it and then signed up with TalkTalk.  So he doesn’t need it.
I’ve been reading about it on different sites, but I don’t understand the jargon.
Do you know anything about it?  Is it any good?  Is it worth the asking price?  Any one reading this using one?
Let me know.

[#3]

Have a look here.  Apparently it currently has problems connecting with certain DSLAM chipsets - but we're talking ADSL2+ which is not here (PN) for some months yet and we're talking about another country (not sure if Optus DSLAMs are used in the UK).  The router is a WiFi machine which retails at c. £99 new (i.e. with warranty) and ebay had it listed for around £11 this morning (there's still 13 hours to go before the auction ends, so prices will go up).  Some more advanced router settings are difficult to configure if you're not technically savvy enough and some firmware updates have been problematic.
So on the face of it at £35 is not a bad punt, but will your friend have it back if it doesn't work for you?

[#4]

Hi, just catching up
@MickKi
Interesting, have to do a bit more digging.
@maranello
Hi, in view of everything, I'd guess 2, try another router and I'd pick it up in your thread Fitting Filters just to keep all the info. on your problem together. Also out of interest report the Firmware version (of both) as well.
@Jameseh
If several routers were reporting Trellis Off, and the problem was still there, my money would be on a Faulty Line Card (DSLAM), if the problem went away, a bit more analysis would be needed (see what the trouble free routers reported on another BB line, preferably guaranteed on a different DSLAM).

[#5]

Get a cheap ex-Sky Netgear DG834GT from Fleabay.
It will need re-flashing with the latest Netgear Firmware but Googling will lead you there quickly and easily.
And looking ahead it supports ADSL2+ fine as well. 

[#6]

@ Anotherone
If it were a faulty line card, I'd be expecting to see other issues being reported.

[#7]

Hi James, I'd probably expect that as well, but as I said if several routers reported the same in more than one situation, then the likeliest is what I suggested.

[#8]

I'm not disputing what you're saying at all.  But this wouldn't be on the same exchange, so not the same line card.

[#9]

Sorry, maybe I didn't explain it well to start with. Undoubtedly the best way to be sure you're not on the same line card would be in a different exchange, I did think of saying that, but decided it didn't need saying. No probs, we're both agreeing.

[#10]

Sorry, I thought you were on about the different forum members in here reporting that trellis was showing as being off.

[#11]

Also, it may be related to a compatibility issue between router and DSLAM chipsets?  Somehow I find it difficult to believe that trellis is off.  I would have thought that it is always on, since (in my limited understanding) there are no downsides to it.