I'd say it was at about 1000ft, and definitely had four jet engines. The 'props' were very small props I could see spinning in front of the pods I mentioned at each wingtip.
It looked most like an AN124 in wing configuration and landing gear arrangement, but had the aforementioned pods.
I'm no expert, but I'm fairly sure it wasn't a C5 Galaxy because of the landing gear layout.
I'll find out the hard way (ringing the airport, believe it or not!) if I can and post the response here.