Hi! My 6 week old baby has started wriggling (still on his back) to the bottom of the cot, or sometimes he will wriggle so he is laying sideways in the cot. He is currently being swaddled. Do we need to stop swaddling him with his arms in? He is not currently showing any other signs of rolling.

Most babies do not roll to tummy intentionally before 3 months; however, some babies do roll & wriggle, especially to the side (or other parts of the cot), at a very early age. This is not unusual.
There is no need to stop your baby from wriggling & changing his position, but it is important to make his environment safe in light of what he is doing.

Often this can mean that baby is soon going to be rolling.
Some babies do not respond well to wrapping/swaddling & prefer to have their arms free.         
Some babies like to touch their face or suck fingers when settling.
**Try settling him without any swaddle, or wrap with his arms out.
https://rednose.org.au/article/wrapping-babies

Are you using blankets?

How does he go with tummy time when awake?
https://rednose.org.au/article/tummy-time-is-good-for-baby-because
Always place baby on the back for sleep.