As soon as I plug my drill into the mains it starts spinning slowly but won’t stop completely which isn’t ideal when trying to use it, how can fix it?? Could it just be some dust has got into the trigger or something?
My old B&d drill had a small knob on the front of the trigger. When it as screwed in (turned clockwise) it would pull the trigger in. If yours has this function try rotating the knob counter clockwise. As other have stated it is possible that debris is in the switch. Try to manually pull the switch out and see if it stopped spinning.
Quick test to see if it's just got a bit dusty/clogged.
Unplug, press & fully release the trigger rapidly a dozen or so times.
If that doesn't make any difference whatsoever, then replace the switch mechanism - $£€ 25-30 - better safe than sorry.
If it does make a difference, even if not completely cure it, then invest in a can of contact cleaner - $£€ 5-10 - Don't spray with power connected, allow plenty of time to evaporate before re-connecting. You may need to disassemble to reach the switch properly.
(I'm assuming this is a variable resistance, slow-start of some sort. If it's not, just replace the switch.)