I overstayed the three hours parking allowed at our local car-park. It is clearly signposted and the mistake is all mine. I have received a parking enforcement notice from Civil enforcement ltd of Liverpool, saying they require payment of the parking charge notice in accordance with the parking terms and conditions stated on the signage. They are offering a discount from £70 - £40 if I pay within 14 days. They are threatening debt recovery Agencies if I don't pay.

Is this legal and do i have to pay??

If not would it be worth the hassle of ignoring their threats?