Odd behaviour

[Brewers23]

I am using Stellarium to drive my Skywatcher EQ3 Pro mount via ASCOM on a PC. The PC is not normally connected to a network. Yesterday evening I selected Capella, when I slewed to the correct RA/DEC, the telescope was actually pointing at an RA approximately 1 hour behind Capella’s real position. There wasn’t an issue when I used the same setup last Saturday. What changed between those two sessions is we put the clocks back on Sunday morning. I suspect that this is the root of my problem. My question is, what do I need to set up in Stellarium to ensure that I am on GMT rather than BST?

[gzotti]

The timezone. If you have configured it as "Europe/London", time in Stellarium should automatically be correct if your computer also shows the correct zone time.
I don't know if ASCOM has separate timezone settings. Or even your mount. Given that Stellarium sends "GOTO RA/DEC" only, the mount is responsible to translate this to sidereal time/hour angle.

[Brewers23]

I used the handset to check the date/time and DST status on the mount. DST is set to off, date and time were correct. I have deselected enable Daylight Saving Time. I have also set up date/time on Windows 10.

[gzotti]

Did you also go through all ASCOM panels? And does your timezone in Stellarium show as "Europe/London", resulting in "UTC" display? After setting the mount with its hand control (1 or 3 stars), I see no way this could happen.