As an update, I sent them a final 'case update' saying that I was going to issue a claim at the CAA so please could they send the initial case information which I sent, as this is required by the CAA to help facilitate the claim. I do not have a copy of this to hand, as this was typed directly into their website form. (Silly I know, I have kept copies of all other correspondence).
They responded that I would need to go through GDPR. In other words, they are making it as difficult as possible to pursue my claim.
The next steps are that I will send a letter to the office of the CEO, and I will file a claim with the CAA.
From a precursory read of statistics from the CAA from last year, they upheld around 80% of claims against Aer Lingus. Which is far higher than other airlines.
This is a complete waste of time, but sadly for Aer Lingus I have time on my hands at the moment. Even as a lawyer, I have never ever had dealings with such an infuriatingly obstinate and neglectful organisation. I will never ever ever fly with Aer Lingus again. I'd sooner catch a ferry.
Just as a matter of interest have you confirmed that the flight was either operated by EI or that they are liable? If the flight was operated by BA there's a very good chance they're not liable.