Thank you all so much for your replies. We monitored him at home until about 3pm and then he started racing around knocking against the walls & kitchen cupboards & we decided we to take him to the vets. He always likes to snuggle up on our laps & have a cuddle but is never too keen on being picked up & wi usually wriggle around, when I picked him up however he just kind of went limp in my arms & 'clung' on to me (wrapped his front paws tight around my arm). He also goes wild for food (we can't even verbally day the 'f-word' in our house as it starts a twirling, leaping frenzy of excitement) but when we mentioned it at around 2pm, which is his snack time) he simply wasn't interested.
The vet checked his temperature, ears, eyes, mouth, had a good feel of his body/legs/tummy and listened to his heart-all apparently fine. She did agree that he seemed skittish & was strangely shaking his head/licking his lips etc. She suggested he had maybe eaten something he shouldn't-obviously we can't 100% say he hasn't eaten anything when out walking (though he definitely hasn't had anything he shouldn't in the house) but he was on his extender lead this morning for his walk & apart from telling him 'leave' the odd thing (plastic bottle, plastic bag) I can honestly say there was nothing I noticed, and I do watch him like a hawk, but I also know you can never say they didn't eat something!! He's going to stay in tonight (it's a vet hospital) and be put on a saline drip in case of anything to flush out. We're just heading back with
some food supplies for him & his blanket and a few toys. We are so worried about him. We couldve taken him home and kept an eye on him but to be honest I could not bear to see him in discomfort without at least trying to do something for him. We'll ring up later tonight for an update & the vet said they can do a blood test tomorrow if we want-which we do. Until then we're heading home to an empty & undoubtedly quiet house-which will be just horrible.