Rated the 4th best degree in America to obtain, even amongst institutes like Harvard and MIT.
As its a broad subject upon graduation you'll be able to apply for almost every computer based job plus if you're maths is good (some courses teach a lot more maths than others so this is worth checking out before applying with a university) you may also land a job with a banking firm. There are a variety of jobs linked with the degree - web designer/developer, software engineer, project manager, network administrator, etc..
Here is a full list of information related to Computer Science - as you can see from the graph - the demand for CS graduates has flown up, as it has across the globe, which is expected considering almost every industry now uses computers and interactivity and simpler communication will be the future.
http://www.itjobswatch.co.uk/jobs/uk/computer%20science.doThe average
starting salary in the UK is £40,000 including London, £35,000 excluding London. This is rising faster than the increase on other jobs in the UK. Some salaries go upto around £80,000.
10% of jobs in CS offer a salary of more than £70,000. Obviously you need to be well qualified or have a lot of experience to demand for such a high wage, as in any other sector.
Down below you can see how what skills are most in demand. Which are the most wanted programming languages for a possible employee to have.
Java, C++, C#, SQL, C, JavaScript, PERL, PHP, Python make up the majority. (I'd assume every Computer Science course in the UK teaches either Java, C# or C++ - more than likely the 3 of them. If not then learn them in your own time. It'll only prepare you for the future better and once you get an understanding of algorithms and putting coding into practice then moving from one to the other may not be as difficult).
You'll also see a list of job titles possible for CS graduates.
In my opinion, as I'm doing it myself in September, it can be very rewarding but its going to depend on whether or not you put the effort into learning the stuff to get the rewards at the end of it. Dedication is key, like anything else in life.
As its also very highly regarded world wide you're not only limited to getting a job here either. It opens up a lot of possibilities and you could set up your own business in a certain field - web design, graphics design etc..
Its entirely upto you. If your committed then do it. If not then maybe something else which you're more committed to is for you. All the best.
PS. Also, as the person above said, you're not guaranteed a job. You're not guaranteed a job in any sector in life. The only way you'll get a good job is through hard work, making sacrifices elsewhere, dedication and a willingness to learn.