I hope this post doesn't break MN (it's so bleedin' long!) but there's been a lot I've not responded to as of yet and whilst I'm not going to even attempt to link all the comments all beautifully to individual posters, I'll try and respond as comprehensively as I can!
And apologies for not getting back sooner - worked from home today but was bashing away on my laptop for hours on end and really really busy.
Prior to the surprise gift of this text yesterday, DS and XH were indeed making all arrangements for contact etc entirely between themselves so I can’t 'start' doing something that we were already doing.... already. That scenario will continue in exactly the same way following this unexpected blip in proceedings.
Domani I appreciate your further comments 
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Thank you Puppy and I can reassure everyone that I am about as far from having a nervous breakdown as anyone has ever been. I’ve got every right to be utterly pissed off after something like 9 months of wonderful radio silence from DH, to be summoned out of the blue to do his bidding when it has absolutely nothing to do with me. The concept of being responsible for the things you yourself decide to do is clearly not one XH is familiar with.
It's a miniscule 5 mins car/taxi journey from hotel to train station OR venue and since all DS needs in his 'overnight bag' is a bloody toothbrush XH could quite easily get him if he wants him to be able to drop his bag, or meet him at the venue in his car and have him put his bag in the car until the concert finishes. So there's absolutely no need for anyone to drop DS on the doorstep of the hotel. It's utterly bizarre and easily managed through a multitude of other options.
Info on the hotel anyone?! I thought I’ll have a look at the actual hotel. Holy Christ the reviews are bloody terrible. Ranging from "Disgusting filthy interior with stained mattresses", "inadequate fire doors", "looks like an old mental hospital inside", "car park is an unlit warehouse unit strewn with rubbish", "no central heating", "freezing cold" (I could go on)! Bloody glad I’m not staying there. Sounds like camping in a cowpat-strewn field would offer more hygiene and comfort.
I actually don’t think it’s to wind me up. In his mind he sees NO issue with what he’s asked demanded. Frame it that it’s for the benefit of his son and then I can be made to look like a truly awful person to his wife and the rest of his family (once again as I'm sure this is an ongoing theme).
“Sometimes I visualise threads like this as a gaggle of hens burbling and flapping and pecking at anything that might be edible” - Yes! Fabulous analogy 
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“Fascinated to see that defending a child against unwarranted attacks on his integrity and venting frustration with a useless and neglectful (to DD) XH is now apparently a symptom of "having a breakdown". Indeed.
So, ready for an update?!
So I waited until mid-morning today (Fri) to send my text (heh heh) and simply said along the lines of 'no I can’t do it, suggest use of trains/taxis'.
He actually replied (!) within the hour (God loves a trier!): 'It would be so supportive for [name of DS] if you transport him to the hotel. Why can’t you help DS?' (as you can imagine I was holding back the tears at this point, picturing poor DS having to ride on a nice train and get into a perfectly lovely taxi - the trauma, the injustice! Will DS ever be the same again?).
Knowing this would be the last reply I’d be sending on this subject I simply said “Your outing, all aspects your responsibility”. Hopefully that will be the end of it and if it's not, I won't be replying anyway, just completely ignoring. I can imagine him receiving it at work today and moaning to his work colleagues what an utter bitch his XW is not helping her own SON oh it's so awful! Arsehole.
He replied again after this (I kid you not - he must be doing the ‘Manipulation’ Scout badge or something): “I’m staggered that you won’t help your son out. I’ll talk to him about the arrangements [badmouth you to him]”.
I have ignored and will continue to ignore. Silly man.
I spoke to DS when I picked him up from college and said that I was not able to help with transport and also it’s totally ur dad’s responsibility to make all the arrangements needed for an outing that HE has devised and it’s nothing to do with me not caring about you DS. I resent DH most for being happy to use his son like this and involve him in shit that is absolutely and totally unnecessary. I'm not sure if this manipulativeness (sorry if that's not a word, my spell checker doesn't like it anyway) is actually him, or wifey. She can be quite horrible (evidenced by DD and by DS). But I think it's him but probably bolstered by her egging him on to 'take a firm line with your XW, DS, DD'. But, meh, who cares anyway. Time spent trying to figure out what's going on in his or her minds is not time well spent.
So no doubt he’ll have to disturb the moths in his wallet and pay for taxis for him since apparently he can't make the 5 min drive to the train station to pick DS up himself and would prefer me to drive into a mental busy Xmas city centre and do it for him. Lordy [shakes head].
Thank you to one and all for the engagement on this mini journey of extreme annoyance! Let the lines go dead again henceforth!