Thanks ladies and sorry I haven't replied earlier. I've been freelancing at the moment as well as fulltime childcare so rather hectic.
Things have definitely improved here during the day.
I agreed that I would go for the intentional short nap in the morning so decided 9.30 would be our put down time. Bizarrely this week that's resulted in a couple of 2 hour naps and some hour ones. I've decided that if I keep this first nap time as set but let him decide how long he needs to sleep, and 'work it' so that we get at least one long nap between the school runs.
I'm pretty sure he'll start short napping at that time but that would be fine as I'll work out his A to the next nap to get a good nap and hopefully set the second nap then.
Anyway it all seems to be working out fine like this with the first nap at the set time and letting him sleep as long as he wants. Fingers crossed and thanks everyone for your help.