I hope this is a really dumb question and someone can answer quickly.

I was trying to change UV's of an object and I must of hit a shortcut or something because everything else has vanished.

i can see everything in the outliner, select and all the visibilities are set to on. In the viewports show tab, All the different object types are set to on, so i should be seeing everything, and all the layers are activated too.

have i entered some isolation mode or something?

Thanks

... turning off all layers doesnt remove the one object i can see.

Nothing to do with clipping planes as visible object is amongst others