I would be interested to know what you mean by "(permanent) freelance".
If you are meaning that a company is offering you a job, but you must set yourself up as a company to handle your own tax (as per Ryanair), I would be very careful.
The different tax authorities in the EU are getting very upset about this, and in the UK you will have big problems with IR35. Basically, if all of your income comes from one place, you are classed as being employed by that place, and therefore are operating an illegal company from the point of tax evasion.
If you are operating under a lot of zero hour contracts, and can pick and choose the days you want to work, and with who you want to work (i.e. through a number of different agencies), then you can expect to pay as little as 0% personal tax, and 20% company tax.
I would strongly suggest you talk to an accountant, and not rely on pprune for tax advise!