My WAN1 is connected at 2880 Kb/s to BT
G.dmt Annex A SHOWTIME 448000 2880000 SNR 15 Atten 46
DSL Mode: ADSL ONly
Modem Code: Default
Modulation: Multimode

My max download speed achievable is only 1900 Kb/s through WAN1 (forced through route policy)
What can I check/change to improve the speed?

I know there is more information needed on my setup and I would be grateful for any prompts as not sure what is required here.

Try different modulation example set it from multimode to adsl2+ > wan > internet access > details page>modulation
If not helps to get higher speed, let the same settings (modulation adsl2 plus) & Try an other modem code wan > general setup> modem code

Your snr is also high, ask BT why they have set it with 15, it may be a line issue & the modem locked with this snr value by its self, but i think if you change from multimode to adsl2+ it may drop so you will get more speed

I have tried the different ADSL2 and ADSL2+ modulations and none of them allow a connection. I have gone back to multimode.
Should one of these work and if not does it indicate a line problem?
Thanks
Nigel

it can be line problem, it can be the 2860 getting lower speed due to dslam/exchange comparability
that is why there are modem codes to try (at 2860 wan>general setup>dsl modem codes)
http://www.draytek.com/index.php?option=com_k2&view=item&id=1226&Itemid=293&lang=en

With line attenuator 46 you should get anything from 4-7 mbps and i see the 2860 is getting only 2.8mbps ... it can be also line issue so check at BT forums, they are helping
Setting modulation with adsl2 or adsl2+ should also work but for a reason ( perhaps unstable line) the 2860 it locks with G>DMT if you set it with multimode
Have you tried any other modem from your isp?

What do you mean when you say getting only 1900kb/s forced by route policy?
All you need to do is set the parameters of your isp at wan>general setup & wan > internet access ... don't need to change anyhting else at the settings to connect with adsl