My ISP's web site states the ADSL connection settings are PPPoA VCMUX, VPI = 0, VCI = 38. That is what I have used on both my old 2800 and a borrowed Netgear router.

When I allow the 2860 (running 3.7.3.3 firmware) to auto-detect the appropriate settings or WAN 1 it selects PPPoE LLC/SNAP and manages to connect. When I manually set it to PPPoA VC MUX it doesn't connect. Any idea why that might be the case? Should I be OK leaving the router using PPPoE?

Thanks

check if you also need pap or chap with your isp parameters, usually by default with draytek is set with both, if you have TT is using pap i think
Check if have ticked by mistake PPPoE passthrough (WAN >> Internet Access) which most likely could be the case to lock only with PPPoE
however PPPoE is still fine, is not much difference between them apart the MTU sending the packets

Thanks for your help. I obviously got it wrong the first time as, when I tried again, it sorted itself out fine. A case of either being overeager or finger trouble! Apologies.