It's been 7 weeks since he was neuter and thank you for your advice, but I won't be removing him from the rest of them. Firstly, he's only allowed around them when I'm there and I don't actually allow him to play with them. When he stops behaving paternally, I usually put him outside or in another room it's just occasionally that this happens. Secondly, they never seem unhappy with the playing, they actually encourage it often. Thirdly, it would be impossible to keep them apart all the time partly due to house layout, partly due to the fact that they can both open doors and partly because they simply want to be together. I can only really manage this for short periods if I get him settled.
If anything, I'm sure if he is stressed it's down to the fact that we've moved house and there's often change going on while we settle in. Either way, I'll try some Feliway and a change of litter and see if it helps. He's only done it three times, so hopefully if I act now the spraying won't get worse.
Thanks again for any advice given - I seem to have gone more than a little off topic!