Sadly, this strikes me as yet another failure by Santander - I have experience of repeatedly pointing out systemic failures in their organisation at branch/counter level and each time they say they will correct these globally within Santander.
Again in my experience, Swift transfers do tend to take longer if a UK bank is involved (sending or receiving) and in general world wide the sending bank seems not to know what happens after the transfer is set in motion (no auto-feedback or monitoring facility and definitely no "completed" signal at the receiving end - you would think this easy to arrange). The first thing to mention is that you will need good records and also as much evidence (paper, e-mail logs, records of events and times etc., etc.) to maximise the strength of any claim so if you have not done so already make a "report" of your own now because you will eventually have to do this for the Ombudsman (also the bank) and you should not wait for memory to fade and items of record going missing. Secondly, you will have to "exhaust" efforts in claiming from the bank before you turn to the Ombudsman. In practice this means either receiving an unsatisfactory final reply from the bank or none at all - if the latter you must make certain that you send the bank a letter saying you want a reply within two weeks and if none arrives then go with that to the Ombudsman. By all means contact them now and log the issue with them and they will tell you the conditions for them turning it into a formal complaint - you will be given a case reference so be ready to write it down.
Do not leave any costs out, including "pain and suffering" but be careful not to overdo it. According to my experience with Barclaycard (obvious attempt to avoid the implications of the Consumer Credit Act) the bank is likely to take your complaint very seriously once they know the Ombudsman is coming into the frame.
Good luc