in admin > configuration > shipping/ packaging you'll find that you have it set to add an extra 3lbs to each parcel. You need to work out your packing weights (normally about 10% which is written 10%:0 ) and then you'll find that at least the weight will be nearer for you to obtain a quote, although the royal mail only shps 2 kg airmail, above that and you are into parcelforce or (writing your own/ having one written) module territory.

thank you
Philip