Pipe lagging problem

I have spent some time lagging a mains cold water pipe that runs through a cold cellar I am renovating. Previously a great deal of water was condensing on the pipe work and dripping onto the floor. I used high-quality Armaflex insulation, and sealed the slits and joints on this tightly with black electrical tape. However, although the situation is much better, and does not seem to be actually dripping now, if I run my hand along the insulation of the horizontal pipe, I can still feel an amount of wetness, which seems to be actually forming on the insulation now.

Could this be because I have used too much electrical tape, which is now forming another cold surface? I have used a lot in places. Should I put more insulation on to cure the problem?

Insulation slows energy transfer, it does not stop it. If the water is flowing a lot to keep the pipe cold, eventually, the outside will cool off to the same temp as the pipe or stabilize inbetween somewhere.

You'd need to determine the dew point, and the relative humidity of the area. If it is quite damp, maybe a dehumidifier is called for.

Depending on the temp and humidity in the room, adding more insulation might move the outside of the pipe above the dew point. The tape isn't causing it but is helping with the seal. If done right, at least now that moisture is only on the outside rather than being trapped inside (unless the pipe is leaking!).