Vauxhall corsa engine ticking and RPM fluctuating

My engine makes sporadic ticking noises when idling and the RPM drops before returning to normal again. This causes the headlights to flicker and I can feel vibrations in the gearstick. Here are videos of the problem (you may have to wear headphones to hear it). It's a 1.2 petrol engine by the way

https://youtu.be/_jEU31rHQmg
https://youtu.be/NARxMVtPsa0