Hi Pietre, I'm an IT contractor who works in the field you're looking to move into, so I have some knowledge of how things are.
Whilst its easily possible to earn £500 per day as a security cleared Cisco contractor, you have to bear in mind that to earn that rate you may not be working close to where you live. The nature of IT means that most of the jobs are in the city and Thames Valley / M4 Corridor, are you prepared to commute to the city each day?
Also, to earn the decent rates, you have to be a contractor, which means setting up your own company, and doing some financial admin. Also, because you're selling yourself as a 'professional service' you will not get sick pay, holiday pay, a pension, gym membership, or any of the other perks permanent staff are entitled to. You can also have your contract terminated fairly easily, compared to a contract of employment. The contracting life isn't for everyone and if I had a family to support other than expensive tastes then I'm not sure I'd be a contractor.
If you look at permanent jobs then the take home pay tumbles. Granted you could probably earn up to £45-50K+ as a highly rated IT infrastructure analyst in the City, but the chances of earning that outside London are far reduced. As a first job you're probably looking at something like £20-30K, and the nature of IT means that your compatriots at that level will be graduates who aren't afraid to work late and hard to get ahead.
I'm not looking to put you off at all, but I think you should definitely be looking at job availability and chatting to a few agencies about the future prospect of work before committing yourself to something.
I wish you every success!
Andy