Don't worry, it's not about being agressive, it's about standing up for yourself. It's extremely unlikely/probably non-existant that the P + d ticket would ever surface again, I would miss visiting the parking shop as the assistant probably woudn't have a clue where your 'lost' P + d ticket went, so that would be a waste of time. In this case, if RH2000 wishes, to go for the throat with the stage 1 complaint (make sure you have times, dates, the name of the idiot who took your ticket, etc) as the clock is now ticking. As Ting mentioned, not the Parking Complaints dept, but the normal complaints. Most local authorities would rather see this solved ASAP as to them it could be 'politically sensitive' especially if it goes down the Local Gov Ombudsman route. Make sure you send your letters via recorded delivery and take the persons name if you speak to anyone from the council over the phone.

If it's issued by the Local Authority, you should try to make a formal complaint with the council's complaints dept officer, under stage 1. There certainly is a case to officially complain due to a) 'admin mismanagement' and b) being treated unfairly (your valid display ticket 'going missing'). If you get hounded by bailiffs, you need to write to them explaining the new circumstances. They are then legally bound to 'pause' until the case is resolved as this is in dispute. When anyone makes a formal complaint to any local authority they are duty bound to respond in 28 days under the Local Government Act. This goes in 3 stages ending up with the Local Government Ombudsman, high court, etc. My wife had x3 parking tickets issued against her from 2001!! Only last month, the case was finally dropped because she made a formal complaint. If it's a private ticket, you may find it more harder as they are private companies who are obviously in it for the money. There should be some regulator, that I'm not sure of. Someone on this forum may know more than me on that subject. Don't be scared. Whatever the outcome, you will become stronger! Good luck.