Studying for a master's in Computer Science after a bachelor's in Physics
Given you can get a first in your BSc in Physics I think it is OK to move. You have a strong written indicator that you know your Maths for an industry person. In addition, you can legitimately claim you left because you liked something else more rather than you leave suspicions you left because you could not handle it.

Having said that, I would personally stick for an MSci in Physics because: 1. It is significantly less common than CS and 2. a Mathematics/Physics education is much harder to acquire later in life (To put it bluntly: People don't catch-up on their PDEs). You say you have the opportunity for a year-long software development project. This is very good and gives you a great foot-hold for future SW development work.

Finally it is important to note that "a software related position within the information sector of the space industry" is a rather broad thing. If you want to do information security, image recognition or something equally specialized you should definitely focus on a specialized MSc. If you want to do simulations, reliability, controls, etc. actually sticking to your MSci might be a better thing (given you know how to code :) ).