A parking fine results from breach of contract. So if you use a car park which requires payment, if you either do not pay or you do but over-stay, they can fine you. You say you overstayed by a matter of seconds and whilst it is technically a breach, it is very minor so I am not surprised that you are here asking for our view.
They will say 1 second over is still an over-stay and they will say they are therefore justified in fining you. You could argue that the overstay was so minor as to not justify a fine of that severity. You would make them an offer to reflect this, or simply refuse payment. If they went on to sue, you would have to defend the claim and in several months from now the court would have to make a decision unless the claim settled in the meantime. They are unlikely to want to incur the time and cost of suing for the sake of £160 so I feel that some negotiation is possible with them. I would say it is 50/50 whether you succeed in a defence or not. Nothing is guaranteed in litigation unfortunately so I cannot say you would definitely have a case if they were to sue.
Further, debt collectors are not bailiffs - they have no powers as such. They will simply try to collect the money their client thinks you owe. You can turn them away if you dispute the debt and they visit you - they can’t enter your home and take goods. They would report back to their client they were unsuccessful and it’s then up to their client whether to take matters further.
They will send a letter before action to you if their debt collection attempts fail - which is required under the pre action protocol to give you the chance to avoid court action. They usually give you 14 days to pay before they will take civil court action.
If they do sue, you will receive court documents (a response pack) which you must complete and return to the court. It is a tick box exercise for the most part and there is a short section to write a defence which is easy enough though please feel free to come back to this site if you need any more help.
You should not ignore the court papers as if you do, the claimant will apply for judgment in default meaning they win and you would not be allowed to defend the claim.
A claim will also take 9-12 months to be decided at court. If you lost then you would get 14 days to pay the judgment before the claimant can enforce the order, and 30 days to pay in full before it is registered with credit agencies. The claimant cannot recover legal costs if they win, in a claim under £10K (a small claim), all they can claim are the court fees and interest.
The hearing (if the case gets that far) is likely to be held remotely, it's you, a district judge (who is a practising solicitor or barrister) and someone from the claimant company. The Judge decides and if you lost, you get 14 days to pay the sum. If paid in full within 30 days then nothing goes on your credit record. But certainly I think you would succeed in a defence, just to be clear.
To given you an idea on what they can claim (if they sued), it would be the £160, plus the court issue fee of £35, if the court lists a hearing there is another fee of £35, and interest at 8%. If they use a law firm they can add on costs of up to £260. So this is the risk to you if you choose to defend the claim and the defence loses.
I can assist you going forwards if it gets to the point they issue a claim.