Under the NHS the orthodontist/dentist is free to choose whatever brace they wish to use. They are not under an obligation to use or offer any particular brace. A good ethical orthodontist/dentist will discuss all the possible types of brace that can be used for your problem, together with the risks and benefits of each one.
There are often also different ways that your teeth may be improved such as simple straightening or full bite correction. You should be wary if you are only offered one option or one type of brace. It is always advisable to ask the orthodontist/dentist how much training they have had in orthodontics and the brace system being suggested.