The firmware (for the 2860 series at least) has an extra "BT" version on the UK site vs. the Draytek FTP site, and the BT version is the recommended one on the UK site. The BT version seems to be released a few days after the others (7 Jan 18 vs 27 Dec 17 for 3.8.6 v03). What is the difference? I haven't noticed any significant difference in ADSL use between the v03 and BT 3.8.6. Thanks

The BT firmware is specifically tested on UK lines, tweaked with UK settings and also includes
all of the extra dev/features for SIN498. This may not always produece different line speed
results especially on good lines and also much of is more relevant to VDSL than ADSL. You should
always use BT firmware in the UK.