Do I need to get Building regulation approval for converting my garage into an additional habitable room such as a playroom, study or bedroom?
I’m sure that you do need such an approval, otherwise your bedroom / playroom / study will be considered as illegal. This can cause problems in future in case you decide to sell it. However, it’s not impossible. If you don’t want to build concrete walls, you can hang industrial curtains (e.g. https://www.curtain-and-divider.com/). They are stronger than normal curtains and are not too expensive.
After you get your approval, maybe you think about renovation of your garage. Maybe you have holes or crack in your walls that you need to fix. I had this types of prolems in my garage recenlty. So I’ve been searching site that can help me on how to fix a wall . And I’ve found one. You can follow to the link yourself to get more good tutorials.