You can look at the System Event Log - via Administrative Tools. In there are entries for Microsoft Antimalware. There are different types:

1000 - start of scan ???
1001 - end of scan ???
1013 - update - no new definitions???
1015 - update - new definitions???
2000 - ???

At the moment I can't find a definition of the various event log entries MSE uses.

In reply to a post by Garyilka:

Hmm - strange. I have defender on three laptops and two desktops

Crossed wires?- I'm talking about MS Security Essentials not MS Defender

Sorry - I started off talking about MSE then managed to confuse myself into defender.......

MSE on two laptops only at the mo........

Thanks for all your input guys, I'll see how it goes in the next day or so !!!!!!!

Panic over - it must have updated when I switched on this morning!

Now showing:
version 1.79.530.0 created on 25/03/2010 at 21.48