Chilli heads.

Attempted to overwinter them, seems to have worked as small leaves starting to form but looks like it's got a bug infestation, any thoughts?

Definitely looks like some kind of plant louse..
..you need to get rid of them (soon) if you want the plant to survive - what worked well for me was showering off the plant and brushing the little fuckers off with an old toothbrush (you'll have to do this multiple times).
As @edmundo said ladybugs (or other useful animals) would solve the problem as well, but are hard to find this time of year..

Oh, and picked up these seeds last week, will try in a few weeks when the frost has gone as don't have any propagators

You should start rather soon 🙂
Remember you can use very basic stuff as a "propagator" - just need something that keeps the humidity, that lets light in, and put that in a warm spot -
I had much success with just two sips of water in little plastic trays (former packaging of cheese from the supermarket, filled with a few layers of kitchen roll (to keep the water), topped with a layer of coffee-filter-paper (so the seeds don't grow into the kitchen roll) - putting all this near a radiator or another spot that's well over 20°C all the time (hint: your internet router) and Bob's your uncle 👍