trouble starting

when i try to start car there is always a delay when key is turned,this is usually only a second or two and car will then turn over and start ok.just lately as it is getting colder the delay is longer and it has lasted minutes before the key will turn over engine and start(all ignition lights etc come straight on).
could this be faulty ignition switch or a faulty sensor for ecu control unit?
any ideas what this could be?
thanks alan.