Thank you for your advice. Definitely an OT spiral as has been going on for such a long time now. Have been working on getting him down earlier first thing in the morning, but still only 30 mins at the moment.
Today he did his 30 mins, settling himself fairly easily but then couldn't be resettled to extend the nap. After trying for 30 mins I got him up but he lasted 15 mins before getting cranky again, so it was back to bed and he's now just finished his second 30 mins. Still messy, but at least it means I can start working towards a more consistent 3.5 hour eating pattern like you suggested instead of him crashing due to tiredness on an 'early' feed.
I've been putting him to bed earlier, by 6.10pm for the last 3 nights and he's gone to sleep independently within 5-15 mins, which is something to celebrate. Down to 2 NWs but he's now started waking earlier - anytime between 5.15 and 6. Not sure how to tackle this as I haven't been able to resettle him to sleep. Is this also just an OT issue which will only sort itself once his naps extend?? Seems I get him more sleep at the start of the night, only to lose it again first thing in the morning.