Free Traffic Legal Advice

A good first step, 'Plan A' as it's often referred to, is to speak to the manager of the Waitrose store, taking along a receipt from the shopping done in their store on the date in question, and asking if they will intervene. Be polite but persistent.

If you do not get anywhere with Waitrose, then make sure you don't miss Britannia's deadline to appeal. They do not seem to be seeking to use Schedule 4 of the Protection of Freedoms Act (PoFA, there's a link in my signature at the bottom of this post) to hold you liable as the registered keeper, so you could appeal as the keeper along the lines of the below:


If appealing online, be careful there are no drop down/tick boxes that cause you to identify who was driving, and keep a close eye on your spam folder for their response. If they do not respond within 28 days, chase them.

OP, the driver was a patron of Waitrose and can demonstrate this with a receipt or similar?

Those managers are either ignorant or lying. There is a very well established procedure under which Waitrose can and does regularly order Britannia to cancel overstaying tickets for Waitrose customers. Email a copy of your Waitrose receipt and the parking ticket to customerserviceteam@waitrose.co.uk and ask them politely to cancel the parking charge because you are a loyal customer who thought there was a 2 hour limit and can’t afford to continue to shop at Waitrose if the bill comes with a £100 surcharge.

The above assumes you were in a Waitrose car park, of course.

Yes, the receipt can be presented to Waitrose’s customer service. I guess,  this route is worth trying as well, but don't want to get my hopes high. 
Someone, I know, an elderly gentleman, lost a sense of time in the Waitrose cafe, reading a paper after food shopping. He had written a letter to customer service saying exactly what you suggested. They didn't cancel the PCN and he is shopping somewhere else now. I wish I had known about the FTLA back then and could suggest appealing it.

My most recent Waitrose / Britannia experience concerned a customer who bought a newspaper and a coffee every morning for a week and left his car in the Waitrose car park for 2 hours while he worked out in the gym next door. Waitrose cancelled the PCNs without a quibble.

What difference does it make whether the driver spent 50p or £50 at Waitrose? Is a patron not a patron if they don't spend more than a minimum amount?

Hi guys!
I have an update on my case.
Today I received the Final Reminder from Britannia in the post.…together with the Waitrose customer service response to my email. They decided to arrange for the fine to be waived for me on this occasion as a gesture of goodwill. Emailing them worked! Thank you for your advice! None of the 3 managers from Waitrose even mentioned emailing customer service about it.
I am very happy that I don’t have to continue battling with Britannia. Saying that, would you know, if I must notify Britannia about Waitrose’s decision to cancel the notice? There is nothing mentioned in their email.
Regards,
Dot