Thanks for all the replies :)
Christmas - that was my instant thought about pull ups and no, I won't be going down that route. Plus as you quite rightly say, it will just make ds2 be GUARANTEED to not use the toilet! This was mentioned by the TA in his class, she's lovely and has been dealing with him but I'm not sure if they've had problems as bad as this before? As for how they go to the toilet, do you mean how it works at school? If in the classroom they can just go I believe and there are toilets almost within, just to the side, but if they are in the hall or something like that, they just need to tell someone they are going to the toilet (but ds2 would never do that). From the playground they can just go in and get a drink/go to the toilet so no problem there. NOt sure about set times or anything although they have prompted him more because of the problems. I'd be more than happy to be called to sort him when he has accidents however with the number he has, I'd be better off staying for the day! (not sure they'd want that with all the little ones I look after with me) Oh and yes, I totally understand the thing with another adult present which I guess is where problems arise as they probably can't always do that.
teaguzzler - that would be great to have someone who would be willing to clean him up properly, hoping that he wouldn't react in the way he can with me at home (as doesn't like being wiped so much but it has to be done!). I totally understand how school feel awkward about all this. I'm a childminder and work alone so worry about false allegations etc. but I also always do what parents ask if it's in the child's best interest but having said that, I'd feel more comfortable cleaning an older child up if it was one who'd been with me for many years (i.e. several been with me since babies, some since 8 weeks old so would feel more natural than with someone who started with me since they were school age IYSWIM).
Wolfiefan - I guess they can but I know that doesn't work for me at home, unfortunately
Peanutbutter - thanks so much, I'll check that site out. And yes, I do believe he's withholding so just bits of poo come out and when that happens, I get him on the toilet but often the moment has gone and he spends ages on the loo but nothing comes out. I then clean him up and it all happens again later. For example, earlier I just guessed he was holding it so picked him up and rushed him to the loo (thank god I have a loo downstairs as I'm pregnant and couldn't be doing with carrying him upstairs all the time!), managed to not get it in his pants as was just in time, encouraged him to get the poo out in the loo (said he couldn't but I sat there with him, put the tap on making him wee then he relaxed), he did a little one, promised he was done, I wiped him and washed his hands with lots of praise for getting that bit out. A parent arrived to collect their child whilst I was wiping/washing hands so then went through and were gone within about 5 mins. Once I shut the front door I could smell poo and yep, he'd done some in his pants again that soon! Anyway, will speak to school again and talk about the school nurse. His bottom is clearing up very well now but I'm just not sure what to do about sending him in tomorrow? :(
jojane - that must have been really hard for you, pleased they worked with you to help the problem. As my ds2 goes through phases, it's hard to know what's best to sort the problem, a couple of weeks ago he was fine with no accidents, now this again.
Abby - when I saw the GP about it in the summer, he didn't think he was constipated but referred him to the Paediatrician as felt it was psychological. Paediatrician agreed and said she didn't feel it was medicial and referred him to CAMHS (as had other behavioural issues). I strongly believe that it started due to him being anxious about starting school and not being with one of my mindees as we chose to put them in different reception classes. This mindee started with me at 8 weeks old and has been with me full time apart from my ML. So ds2 has grown up with her around since he was 10 weeks old. He had bad speech and language difficulties which caused him to be mute in preschool, he found it so hard to communicate with people he wasn't familiar with (as other people didn't understand him). When he started nursery and was with this mindee, he was a totally different child and would be more himself in that environment (plus attached to the school he's always known). But they became each other's security blankets (more him) and their relationship was a bit too intense and he wouldn't make new friends so we decided to split them. I think once he knew about this, he got really worried about school and this could have started it off (was the right decision though as he's done amazingly well socially since starting!). Before he started school he was having up to 9 accidents a day :( Once he started school it soon became a lot better (like he realised he didn't need to worry about school afterall, he settled MUCH quicker than was expected!). But every now and then it starts again and we get locked into this cycle IYKWIM. I'm not saying he's never constipated but it doesn't appear to be the issue. I do think sometimes he's holding it in for some reasons although other times I'm sure he just doesn't feel it. Thanks for the tip about letter from Paediatrician, as we've got an appointment on Monday I'll ask for something to be sent! :) And yes, using Bepanthem now which has been amazing at clearing it up, will continue to apply as a protective layer too.
Anyway thanks again for taking the time to respond to my OP. I've now got to decide on whether to take him in tomorrow or leave it and arrange a proper meeting with them to discuss the situation now it's got to this level.