Hi there!
I work at a nursery, so, I might be able to give you a little help. I've only been at my nursery for about a month, and I'm sure all nurseries are different, but, I'll give it a shot anyway.
I'm guessing they'll do a home visit, just to see what his favourite toys are, his favourite foods, things he likes doing, how he socializes with the person doing the visit, more than likely, because the person will be either the manager/owner or the even child's key worker. Their key worker will be the person who is your child's touch stone at the nursery. There will be plenty of people that look after your child, but, the key worker will be the person to tell you how his day went, will do observations on your child, and will keep a learning journey on your child. The learning journey's a sort of scrap book and a progression of how your child grew in their nursery. At our nursery, the staff take photos and also type up their observations and put them all into the learning journey. It's really sweet. They take photos from the child's first day, and it just goes on from there.
We all follow what's called EYFS(Early Years Foundation Stage) and here's a link for all of the stages and what they mean.
http://nationalstrategies.standards.dcsf.gov.uk/earlyyearsEvery nursery's a bit different in their structure. At ours, it's "child centered". For example, today, we made trains(this week's theme was trains) out of the shapes circle, square, rectangle and triangle. The children were given the shapes, glue and some paints, and they were allowed to glue the shapes how they wanted, and painted their art how they wanted to do it. We didn't direct them in how or where to put the shapes down, just let the children's imaginations direct them. Then, we had lots of free play(it was a sunny day, so, we took advantage of it.), we took a few weeds out of our garden, they had their lunch(which is called dinner here) etc, etc.
Everyone that works with children in the UK has to have a CRB(Criminal Background Check) done before they're left alone with the children, and they're either working towards what's called their NVQ2 or 3, or they've already got them under their belt. NVQ means National Vocation Qualification, which assesses that you're fit and qualified to work in your chosen field.
I'm sure that the person coming for the home visit will tell you pretty much the same things, but, I'm hoping this will help you and make you feel more at ease. I'm sure your son will be well cared for! You'll learn more once you can visit the nursery. If you don't feel like they will be a good fit, though, go with your gut instinct and move along.