NHS- UK national health service.
Scans- it depends where you live and whether your preganacy is straightforward or not. In London, for example, you get a routine scan at 12 weeks and 20 weeks (for dating and anomalies, respectively.) In Scotland, you get a 12 week one, but not a 20 week, and in Bristol, and most parts of the country, in fact , you get the 20 week, but not the 12. The 12 week scan, to be honest, is not all that useful, unless you have no idea when the baby was conceived, as it can't show up anything much; the 20 week, or 19 or 21- thereabouts- is essential, and it is shocking that they do not offer it in some parts of the country, as this is when you can see if there are any problems and be prepared for them if there are. It is very detailed.
However, if the pregnancy is problematic, as my second one was, or if you have had problems in the past, such as miscarriages or fetal abnormalities, you will be offered additional scans- I had one at 7 weeks, as I was extremely sick, then the 12 and 20 weeks, and also a growth scan at around 30 weeks.
Does that answer your question?
You can, of course, have scans privately, if you are happy to pay for them, but really, if you are feeling OK, and the midwives have not recommended otherwise, the 20 weeks one is the only one you really need.