My 10 day old newborn will only sleep on his side when in his bassinet. If he's on my bed he will happily fall asleep on his back, will also sleep in my arms/on my chest with no issue Is there anything I can do to stop him rolling onto his side?

When you place him on his back for sleep, does he roll straight to his side?
Are you wrapping/swaddling him?
Have you started tummy time yet?
This can be started from birth & increased as baby gets older.
https://rednose.org.au/downloads/RN0407_22_Tummy-Time.pdf

While babies rolling to their side at a young age is not common, it does happen with some babies.
Some babies do not respond well to swaddling as they like to be able to touch their face &/or suck on their fingers. 
In an effort to do this they sometimes end up accidentally rolling over to their side.

It can help to no longer swaddle baby with arms in or else stop altogether.
General swaddling info:
https://rednose.org.au/article/safe-wrapping-or-swaddling-when-to-stop-and-how-to-select-a-safe-sleep-bag
https://rednose.org.au/downloads/RN0407_22_Safe-Wrapping.pdf

Ensure mattress is firm, well-fitting & flat (not elevated in any way)
Always place baby on his back for sleep.

Have you seen your local Midwife/Child/Health/Maternal Nurse yet?
It would be good to chat with them in relation to settling tips.