Hi Andy,
This could be a couple of things:
1. You don’t say if its one or all lights, so if one then I would suggest poor connection in wiring or possible light switch or even faulty light itself.
2. If all lights, then I would recommend plugging a standard 60watt light bulb table lamp into a wall socket and watching it closely, if it does the same then this is affecting more than one circuit and I would say it is a supply problem from road or possible fusebox problem. This would need urgent repair/ investigation.
When you change to low energy lamp these are more tolerant to supply irregularities as well as normal electrical equipment, ie TV, computer, heater can all have a minor supply interference glitch and go totally unnoticed but a light bulb you would notice much easier.
As for worse early evenings is it possible its happening worse when a cooker, shower or generally more people are using electricity and making a poor connection ark and overheating more affecting your lights making them flicker.
Get checked out as ASAP as possible fire hazard, and check for burning smells or fishy smells around electrical equipment, ie consumer unit