Norwich charges £30 (1400kg MTOW). That is high by the usual UK "decrepit GA field" standards, and is high by the French "local chamber of commerce subsidised" standards like Biarritz etc. But it's not high when compared to most airports that are busy with passenger turboprops and 737-type jets. Lots of European airports charge £50-£150.
£30 is only a small part of the operating cost of a reasonable plane. If you are over 2000kg then you will spend that much per hour in IFR route charges.
What £30 means is that you won't be flying your microlight to Norwich.
But (being the devil's advocate) Norwich, and nearly every other UK airfield for that matter (whose grass gets cut more often than once a year, and whose cracks have been repaired at least once since WW2) cannot make ends meet on the microlight burger runs alone.
This is why every airfield is trying to become "XYZ International". It's not (in most cases, I reckon) that they are desperate to chuck out GA. It's because GA spending is so damn tight, and there is too little of it anyway. The airfield cafe can probably just make ends meet on the chocolate cakes and ham and chips, but the airfield will just rot. Even though the UK is probably the busiest GA country outside the USA, the level of activity is still too low to keep an airfield in business on GA alone.
So business traffic is necessary, but "business" won't go there if the place is decrepit. You won't fly anything half decent (a Seneca, never mind a King Air) to some place ridden with potholes.
UK pilots want £5 landing fees, but apart from fuel sales there is no other income for the airfield.
The business about toothpaste confiscation, GA security etc, is just stupid management. It's simple to set up a "GA" entrance/exit. Security is a business full of small men who feel important, and they make a job out of it. But ultimately it is the management that lets them do this empire building.
If I was going to one of these places on business, I would phone them up and ask for the correct procedure to get through, preferably via one of the clubs.
A PPL at Norwich must be expensive though - £2000 spent on landing fees in the typical PPL there.