BSc Computing (with specialism if it's the one I'm thinking of) is the best bet. ISD isn't the real thing in comparison, although it's certainly a good qualification.
I loved every minute of Computing, and if you are a fan of software dev then you'll definitely love it.
Assuming you jump straight into third year, I'd make sure you were up to speed on Java, C++, and OOP principles. Software development modelling (UML, et al) would also be useful. These are all taught and required. You cover matters such as Component Based Software Development, project management, data protection issues in modern I.T, and dedicated classes in the first semester of fourth year on how to approach your honours project - and your career.
Oh and you're going to have a blast, and a headache probably, doing the Degree project. Group software projects are as close as it gets to the real world. Just don't be the project manager - it will give you many sleepless nights

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As an endorsement, one of my fellow graduates now works for Apple in London, another for J.P Morgan doing projects with back-end and front-end work that make me cry like a little girl in jealousy. I myself decided to start my own consultancy after graduation, offering small businesses the basic know-how of modern I.T. I'm not blowing anyone's trumpet - I'm just showing you the options it gives you.
Edit: As my honours supervisor and course coordinator once said (Dr. Foley): "We're training you to be software developers."