Seems a bit vague!! Guess by the term 'packages' they under 2kg? Royal Mail probably best bet to start with, you can check out the prices for Airmail / Airsure etc , even pay & print out the postage labels & CN22's on their website.
If you are going to be sending more than just the odd package, then I would recommend opening an account with one of the major carriers as you will get a better deal.
If it will be a regular thing then open an account with your prefered courier - this will give you a discount on shipping fees and will automate some of the process for you.