Originally Posted by
craigthemif
You would then have to:
1. clear T4S transfer security to go to Velazquez
2. hope that the Velazquez lounge dragon doesn't say "you don't belong here"
3. find your way to arrivals, clear passport control and then do transfer security again for M gates (as you would have mixed with arriving pax)
Yeah, But personally I probably would and avoid the train. The "find your way to arrivals" part is extremely easy. I've done after I realized I forgot something at main security before. It's just a door you walk through that takes you upstairs to the arrivals stream.