When is £100 really £50

Went to London recently. Drive wise it's about 2 1/2 hours and by the time I normally get there it's near midday and I am hungry. Usually I would park near Tuffnell Park Tube Station as there is a cracking Kebab shop opposite where I can deal with the hunger pains. On this occasion every little piece of roadside space had been grabbed for either parking permits or buy a ticket for maximum 2 hours. Now that is not enough time to catch a tube to central London do my business and get back in time to feed the meter again. I drove round and round the area to see if there was a six foot space somewhere where I could park and believe me it is a big area. There were no car parks anywhere either road level or multi storey. God knows how the local shopkeepers survive but maybe they do from just local residents who use "on foot" as their means of transport. Anyway, I stopped a taxi driver and asked if he knew where I could park and he advised me it would be best to buy a ticket and chance it..it will be o.k. he said. I took his advice and took off for the tube station as I was late. When I arrived back there was the ticket stuck to my screen and I was gobsmacked to find it was for £100. There was bags of room to park alongside this particular road, no problems. When I read it I was gobsmacked on a second count to find that if I paid it in 14 days it will only be £50. Now hang on..is it a £100 fine or a £50 fine or is it just scare tactics to make you pay up sooner ? Fortunately mine is a company car so it will take them longer to find me so they will have to wait for any money which will be forthcoming at the very last knockings, personally delivered to them by me in one pence pieces and I will demand they count it in front of me and give me a receipt !!! Take on or what ?
Beware and take no advice from taxi drivers..they speak with forked tongues !!!