I am sure the visa has now been applied for and is firmly stuck in your passport, but I thought I would add this for anyone coming across this thread in the future.

When my wife and I applied for a Schengen visa through VFS in London, for Spain, the application was delay because they didn't have enough proof of purchase for the flights. We had 'confirmation of booking' print-outs for our flights, but that wasn't enough, apparently. We did ask what else they could possibly want, bearing in mind that most flight bookings are electronic now, and all they could say was 'what you have provided isn't enough'.

We then went back to the flight operator, and found out that, although they don't do it as a matter of course, they can also provided itemised electronic receipts. This is what we sent on to VFS, and we got the visa and passport back quickly afterwards.

It's important to bear in mind that, it's not the Spanish Embassy, but VFS making these decisions about what documentation to accept. I think we may have got a rep on a bad day, and it cost us time and a bit of extra money.