No Merry I'm in Wiltshire.
I think it's dangerous to start putting ideas into parents' heads about what conditions their children may or may not have. I remember being told on Mumsnet that my ds most definitely had coeliac when he actually just had toddler diarhoerra, but for a while I was planning to cut out all gluten from his diet.
We don't know Merry's ds and whilst some of his symptoms might be similar to someone with ADHD, others might not be. After all if I posted about my ds's attachment issues and the way he lines up cans and tins in the supermarket, someone would undoubtedly say that he has autism. Yet I would have failed to mention his good communication skills and ability to socialise and express himself with ease.
I think it's far better to suggest that Merry explore all avenues, which is what I realise many of you are saying it's just that ADHD has been mentioned a few times by different people and it's easy to start then looking out specifically for the traits that match ADHD whilst ignoring the ones which don't.
This little boy is only in Yr1 and school is still a big deal and very new. Lots of little boys cannot sit still in assembly. I am an ex-TA and I worked with children who had special needs. I can honestly say that your boy does appear to be normal. Yr1s find it hard to still still and concentrate, especially boys. Often younger boys will make one friend (usually older but not always) who they absolutely adore and will stick to like glue. My ds was just the same, I too was horrified to see him messing about in assembly and I know from what teachers have said that he could be immature at times and would chat in class and not really put enough effort into his work. He also had a friend called Daniel who he would go on and on about. My ds is also sensitive, like yours and finds it hard to be separated from me. He's very affectionate and emotional.
I can't find out if you have spoken to his teacher yet or not, but a quiet word about how he is performing in relation to the others is a good move. If the school had any concerns they would contact you and trust me, spotting those telltale signs of ADHD or Aspergers or Autism is a lot better now than it used to be and many teachers receive training in this area. In fact if your class has a TA, he/she may well have completed a training course for assisting children with special needs so they might be a good person to approach with any concerns too.
But from what you have said just on this thread, nothing strikes me as out of the ordinary. You say he is well behaved at home, that he is empathetic and conversational and he is capable of making friends. I think the mistake you are doing is to compare him to your other son. Every child is different and you must not think that because one child behaved in a certain way by a certain age that these are the targets your other children must reach. Boys are immature compared to girls and some boys take a longer time to grow up than others. My ds is now 7, nearly 8 and he still puts on a baby voice at times and will behave like a 3yr old but that's because he still craves the security that being a baby gave him and struggles to accept this growing older business.
If you take him the the GP he will most likely be referred to the children's mental health team and the waiting list could run into 6 months. At the age your ds is, it will be very hard for them to assess him properly. I honestly think that if the school are happy with his progress and you know he can behave at home and be socially interactive, then I would keep up the praise and rewards for being good and STOP COMPARING. Enjoy him.