All working well.
A pleasant Mr Kelly installed an ECI modem and, with minimum of fuss, convinced me the DSL lamp was on, and the phones still worked too.
Frustratingly, I failed to manually amend the 7800DXL configuration to use pppoe and WAN port. But having admitted defeat, swallowed my pride, and let the 'quick start' wizard do it for me, all went well.
I have of course no access to stats, but speedtest.net indicates
download of circa 44 Mbps, upload 10Mbps, which ain't bad for 550metres from cabinet. As mentioned earlier I am entertaining guests for the next few days, so will just leave all to one side now. The options for getting stats will be explored later next week.