I've read through all the helpful guidance on this thread, and just want to put out the feelers on my so far unsuccessful claim. I'm reasonably familiar with EC261/2004 having successfully claimed twice with other airlines in the past.

Here's a quick overview of my current claim:

15th July: Booked on BA1495 (GLA-LHR) and BA27 (LHR-HKG). Arrive at GLA to be told that BA1495 is 2+ hours late resulting in missed connection for BA27. Reason given is network wide disruption (edit: short haul network) caused by FLY. Am given option of travelling down on delayed BA1495 and connecting to BA31 (LHR-HKG) on the 16th, or taking BA1483 (GLA-LHR) on 16th and connecting onto BA31. I choose the latter. Nothing said about assistance with transport costs or anything under EC261/2004 (in itself a violation of the regulation). No advance notice was given of BA1495 delay by phone/text, on BA app, website or airport screens. Also, travelling down on BA1483 will result in 5+ hour transfer at LHR as all later flights GLA-LHR are full.

16th July: Turn up at GLA, it takes agents 1 hour at check in to link together PNRs of my two rebooked segments. FLY again cited as the problem. Eventually get onto BA1483. At LHR I approach customer service in T5, I ask for food voucher under EC261/2004. Helpful lady gives me voucher and says my case has not been handled properly as I was given no info about EC261/2004. She encourages me to apply for compensation under EC261/2004. 5+ hours later I eventually board BA31 which leaves the gate 45 mins late with the captain announcing "passenger number discrepancies due to new software", presumably FLY again.

17th July: I arrive at my final destination (HKG) around 21 hours late. I immediately submit EC261/2004 claim through BA website.

3rd August: E-mail received from BA stating the following - "I've investigated your claim for EU compensation and I'm sorry to inform we've refused your claim because you didn’t travel on our delayed flight, BA1495 on 15 July. Under EU Regulation 261/2004, we’re not liable for a compensation payment in this situation." I reply immediately pointing out that the fact I didn't travel down on delayed BA1495 is irrelevant and asking this to be escalated to a manager if he can't accommodate my compensation as it's a clear cut case.

7th August: E-mail received from BA stating the following - "I’ve reviewed your claim and the flight BA1495 on 15 July was delayed because of adverse weather conditions. We always want to maintain a stable operation. This isn’t only because of the disruption to our customers, but also because of how difficult it is to recover from major disruption. I’m afraid we had no option but to delay this flight and we’re not liable for a compensation payment when the delay is due to weather." Well, this is the very convenient excuse of "it was the weather" to invoke extraordinary circumstances exception. The problem is, I was specifically told by several BA staff that the delays were caused by FLY, nothing was said previously about weather, and BA have changed their reason for refusing compensation.

Any thoughts?