Glad your seeing decent speeds Chris P Duck, yes you must be pretty near to a fttc cabinet and have a decent copper line to it.
I upgraded to Zen fibre 1 without doing any research & believing the advertised speeds. On activation zen sent email saying service was live & giving estimated speeds of 15/0.8 Mbps, hardly better than my adsl2 that was stable at 10/1.2 Mbps. I asked to go back to adsl cos I didn't think the service was worth the extra, only if I paid the early termination charge! I pointed out that their advertise estimated speeds were misleading. Their response was that their figures came from BT!
So did the research as suggested on this site, found which cabinet I was on & what the line length is. Turns out I'm connected to a cab 1400m away not the one 100m away, moreover BT won't connect me to it. In upgrading to fibre I've only got rid of 485m of old cable to the exchange.
Initial syncs were 22/1.8 meg which fell over the next two weeks to 13/0.8 meg. A series of quiet line tests soon got to the cause, intermittent line noise. Three BT engineers later, new master socket & back plate, a change of one wire to the bottom of the street (removing approx60m of aluminium cable with copper) & gel (?) connectors at the top of the pole has improved the rates to 20/1.1 meg.
Root cause of the poor speed was given by the first engineer, sections of aluminium cable along the way to the cabinet & BT would replace it cos of the cost!
