This afternoon was mildly warm, cloudy to overcast with moderate wind. No rain. I was passing under those 400kV lines on my bike (normal, not e-bike) and accidentally brushed my fingers on metallic brake levers. Their surface turned from smooth to a kind of "harsh" - I could clearly feel 50 Hz on them! A similar feeling you sometimes have on metallic parts of some electric appliances on mains. No mistake - it disappeared when I passed the place.
While I knew I was safe, it was a bit scary. It's a hill and the lines aren't too high above the road. What's strange - I passed through that place hundreds of times and never noticed that before! Maybe something in the air?
I wonder if anybody ever experienced something similar?

You may have picked up some parasitic (harmless) current under favorable weather conditions and high field strenght (multiple kV/m) to make this current perceptable. It went through your body (head, torso, arms) upon touching the metallic brake handles via the bike frame and tires towards earth.

Next time, take a 5ft fluorescent tube and stick it up under the power lines at night. There's a good chance it will faintly light up.

Maybe the power lines had been highly loaded (too many people using A/C etc.) hence the strong electromagnetic induction? I was riding the same bike on the same spot a couple of days ago and didn't feel a trace of electricity.

I'm not sure if electromagnetic field 50Hz would light up a fluorescent tube. Some microwave technologies do but the low frequency electromagnetic field?

If the field strenght is high enough, it absolutely can. But you need a pretty dark location for that. I tried it at the 400kV powerlines in my urban location but couldn't see anything.

The field that got coupled to you is coupled capacitively, so is only dependent on the voltage and distance and not on the current running in the lines

The current is very small, and to be perceptible it must go through a small spot on your body. It is possible that in previous times you had a more solid hold on the brake lever before entering under the power line, so the same current was distributed on a larger surface area and you didnt feel it

The current may play a role though: If the line is highly loaded, the cables heat up, so sag deeper down so the field becomes stronger.
And it may not be directly linked to the hot weather: the line loading is being adapted according to the weather conditions, so when not that hot operators may have be loading the line more than in really hot weather, the criteria are the real condition of the equipment (the temperature and mainly consequent cable sag is one of the most prominent parameter used to determine safe loading). Some uneven weather may have contributed also: When there was windier at the place the operator is actually monitoring the weather and less windy where you were may make them to push the line loading higher than usual (for the temperature), but still safe, there are required margins to account for such unevenness.

I've not experienced any sensation on the break leavers of my bike, but I cycle to work every morning along side a 132,000 volt transmission line, but I have heard the corona discharges around the isolators quite loudly on damp mornings, when all the homes and businesses are drawing the most power 😎, oddly enough, I don't hear the same thing on the same way home 🤔, the power usage must not be as heavy at that time?

The isolator buzz is very often not corona discharge, but arcing over thin corrosion layer on metal hardware tying the isolator cells together into those chains. The isolator cells form capacitors, but when the the hardware parts oxidize, the oxide layer forms another dielectric barrier in series, so the capacitive current creates voltage drop across it. Because the oxide layer is very thin, it tends to break down and create a small spark. These then create the buzz you can hear. Plus it creates strong RF interference. Very often these hardware parts are supposed to be connected by metal straps, so no voltage could build up across the oxide layer, but these straps then often corrode out and fall off.

And the fact the buzz changes over the course of the day has more to do with the atmosphere humidity and not much with the line loading. Regardless whether the buzz is a corona or the sparking in the hardware, it is related to the voltage on the conductors, not to the current through them. And the voltage does not change with the line loading.